Dato un intero positivo, scrivere una funzione che restituisca vero se il numero dato è palindromo, altrimenti falso. Ad esempio, 12321 è palindromo, ma 1451 non è palindromo.
Pratica consigliata La somma delle cifre è pallindromo o non provarlo!
Metodo 1:
Sia il numero dato nessuno . Un metodo semplice per questo problema è innanzitutto cifre inverse di nessuno , quindi confrontare il contrario di nessuno con nessuno . Se entrambi sono uguali, restituisce vero, altrimenti falso.
Di seguito è riportato un metodo interessante ispirato al metodo n. 2 di Questo inviare. L'idea è quella di crearne una copia nessuno e passare ricorsivamente la copia per riferimento e pass nessuno per valore. Nelle chiamate ricorsive, dividere nessuno di 10 mentre ci si sposta lungo l'albero della ricorsione. Mentre ci si sposta verso l'alto nell'albero di ricorsione, dividere la copia per 10. Quando si incontrano in una funzione per la quale tutte le chiamate figlie sono terminate, l'ultima cifra di nessuno sarà una cifra dall'inizio e l'ultima cifra della copia sarà una cifra dalla fine.
C++
// A recursive C++ program to check> // whether a given number> // is palindrome or not> #include> using> namespace> std;> > // A function that returns true only> // if num contains one> // digit> int> oneDigit(>int> num)> {> > >// Comparison operation is faster> >// than division> >// operation. So using following> >// instead of 'return num> >// / 10 == 0;'> >return> (num>= 0 && num<10);> }> > // A recursive function to find> // out whether num is> // palindrome or not. Initially, dupNum> // contains address of> // a copy of num.> bool> isPalUtil(>int> num,>int>* dupNum)> {> > >// Base case (needed for recursion> >// termination): This> >// statement mainly compares the> >// first digit with the> >// last digit> >if> (oneDigit(num))> >return> (num == (*dupNum) % 10);> > >// This is the key line in this> >// method. Note that all> >// recursive calls have a separate> >// copy of num, but they> >// all share same copy of *dupNum.> >// We divide num while> >// moving up the recursion tree> >if> (!isPalUtil(num / 10, dupNum))> >return> false>;> > >// The following statements are> >// executed when we move up> >// the recursion call tree> >*dupNum /= 10;> > >// At this point, if num%10 contains> >// i'th digit from> >// beginning, then (*dupNum)%10> >// contains i'th digit> >// from end> >return> (num % 10 == (*dupNum) % 10);> }> > // The main function that uses> // recursive function> // isPalUtil() to find out whether> // num is palindrome or not> int> isPal(>int> num)> {> > >// Check if num is negative,> >// make it positive> >if> (num <0)> >num = -num;> > >// Create a separate copy of num,> >// so that modifications> >// made to address dupNum don't> >// change the input number.> >// *dupNum = num> >int>* dupNum =>new> int>(num);> > >return> isPalUtil(num, dupNum);> }> > // Driver program to test> // above functions> int> main()> {> >int> n = 12321;> >isPal(n) ? cout <<>'Yes
'>: cout <<>'No'> << endl;> > >n = 12;> >isPal(n) ? cout <<>'Yes
'>: cout <<>'No'> << endl;> > >n = 88;> >isPal(n) ? cout <<>'Yes
'>: cout <<>'No'> << endl;> > >n = 8999;> >isPal(n) ? cout <<>'Yes
'>: cout <<>'No'>;> >return> 0;> }> > // this code is contributed by shivanisinghss2110> |
>
>
C
#include> #include> > // A function that returns true only> // if num contains one digit> int> oneDigit(>int> num)> {> >// Comparison operation is faster> >// than division operation.> >// So using the following instead of 'return num / 10 == 0;'> >return> (num>= 0 && num<10);> }> > // A recursive function to find out whether> // num is palindrome or not.> // Initially, dupNum contains the address of a copy of num.> bool> isPalUtil(>int> num,>int>* dupNum)> {> >// Base case (needed for recursion termination):> >// This statement mainly compares the first digit with the last digit.> >if> (oneDigit(num))> >return> (num == (*dupNum) % 10);> > >// This is the key line in this method.> >// Note that all recursive calls have a separate copy of num,> >// but they all share the same copy of *dupNum.> >// We divide num while moving up the recursion tree.> >if> (!isPalUtil(num / 10, dupNum))> >return> false>;> > >// The following statements are executed when we move up the recursion call tree.> >*dupNum /= 10;> > >// At this point, if num % 10 contains the i'th digit from the beginning,> >// then (*dupNum) % 10 contains the i'th digit from the end.> >return> (num % 10 == (*dupNum) % 10);> }> > // The main function that uses the recursive function> // isPalUtil() to find out whether num is palindrome or not.> bool> isPal(>int> num)> {> >// Check if num is negative, make it positive.> >if> (num <0)> >num = -num;> > >// Create a separate copy of num, so that modifications> >// made to the address dupNum don't change the input number.> >int> dupNum = num;> > >return> isPalUtil(num, &dupNum);> }> > // Driver program to test above functions> int> main()> {> >int> n = 12321;> >isPal(n) ?>printf>(>'Yes
'>) :>printf>(>'No
'>);> > >n = 12;> >isPal(n) ?>printf>(>'Yes
'>) :>printf>(>'No
'>);> > >n = 88;> >isPal(n) ?>printf>(>'Yes
'>) :>printf>(>'No
'>);> > >n = 8999;> >isPal(n) ?>printf>(>'Yes
'>) :>printf>(>'No
'>);> > >return> 0;> }> |
>
>
Giava
// A recursive Java program to> // check whether a given number> // is palindrome or not> import> java.io.*;> import> java.util.*;> > public> class> CheckPalindromeNumberRecursion {> > >// A function that returns true> >// only if num contains one digit> >public> static> int> oneDigit(>int> num) {> > >if> ((num>=>0>) && (num <>10>))> >return> 1>;> >else> >return> 0>;> >}> > >public> static> int> isPalUtil> >(>int> num,>int> dupNum)>throws> Exception {> > >// base condition to return once we> >// move past first digit> >if> (num ==>0>) {> >return> dupNum;> >}>else> {> >dupNum = isPalUtil(num />10>, dupNum);> >}> > >// Check for equality of first digit of> >// num and dupNum> >if> (num %>10> == dupNum %>10>) {> >// if first digit values of num and> >// dupNum are equal divide dupNum> >// value by 10 to keep moving in sync> >// with num.> >return> dupNum />10>;> >}>else> {> >// At position values are not> >// matching throw exception and exit.> >// no need to proceed further.> >throw> new> Exception();> >}> > >}> > >public> static> int> isPal(>int> num)> >throws> Exception {> > >if> (num <>0>)> >num = (-num);> > >int> dupNum = (num);> > >return> isPalUtil(num, dupNum);> >}> > >public> static> void> main(String args[]) {> > >int> n =>12421>;> >try> {> >isPal(n);> >System.out.println(>'Yes'>);> >}>catch> (Exception e) {> >System.out.println(>'No'>);> >}> >n =>1231>;> >try> {> >isPal(n);> >System.out.println(>'Yes'>);> >}>catch> (Exception e) {> >System.out.println(>'No'>);> >}> > >n =>12>;> >try> {> >isPal(n);> >System.out.println(>'Yes'>);> >}>catch> (Exception e) {> >System.out.println(>'No'>);> >}> > >n =>88>;> >try> {> >isPal(n);> >System.out.println(>'Yes'>);> >}>catch> (Exception e) {> >System.out.println(>'No'>);> >}> > >n =>8999>;> >try> {> >isPal(n);> >System.out.println(>'Yes'>);> >}>catch> (Exception e) {> >System.out.println(>'No'>);> >}> >}> }> > // This code is contributed> // by Nasir J> |
>
>
Python3
# A recursive Python3 program to check> # whether a given number is palindrome or not> > # A function that returns true> # only if num contains one digit> def> oneDigit(num):> > ># comparison operation is faster> ># than division operation. So> ># using following instead of> ># 'return num / 10 == 0;'> >return> ((num>>=> 0>)>and> >(num <>10>))> > # A recursive function to find> # out whether num is palindrome> # or not. Initially, dupNum> # contains address of a copy of num.> def> isPalUtil(num, dupNum):> > ># Base case (needed for recursion> ># termination): This statement> ># mainly compares the first digit> ># with the last digit> >if> oneDigit(num):> >return> (num>=>=> (dupNum[>0>])>%> 10>)> > ># This is the key line in this> ># method. Note that all recursive> ># calls have a separate copy of> ># num, but they all share same> ># copy of *dupNum. We divide num> ># while moving up the recursion tree> >if> not> isPalUtil(num>/>/>10>, dupNum):> >return> False> > ># The following statements are> ># executed when we move up the> ># recursion call tree> >dupNum[>0>]>=> dupNum[>0>]>/>/>10> > ># At this point, if num%10> ># contains i'th digit from> ># beginning, then (*dupNum)%10> ># contains i'th digit from end> >return> (num>%> 10> =>=> (dupNum[>0>])>%> 10>)> > # The main function that uses> # recursive function isPalUtil()> # to find out whether num is> # palindrome or not> def> isPal(num):> ># If num is negative,> ># make it positive> >if> (num <>0>):> >num>=> (>->num)> > ># Create a separate copy of> ># num, so that modifications> ># made to address dupNum> ># don't change the input number.> >dupNum>=> [num]># *dupNum = num> > >return> isPalUtil(num, dupNum)> > # Driver Code> n>=> 12321> if> isPal(n):> >print>(>'Yes'>)> else>:> >print>(>'No'>)> > n>=> 12> if> isPal(n) :> >print>(>'Yes'>)> else>:> >print>(>'No'>)> > n>=> 88> if> isPal(n) :> >print>(>'Yes'>)> else>:> >print>(>'No'>)> > n>=> 8999> if> isPal(n) :> >print>(>'Yes'>)> else>:> >print>(>'No'>)> > # This code is contributed by mits> |
>
>
C#
// A recursive C# program to> // check whether a given number> // is palindrome or not> using> System;> > class> GFG> {> > // A function that returns true> // only if num contains one digit> public> static> int> oneDigit(>int> num)> {> >// comparison operation is> >// faster than division> >// operation. So using> >// following instead of> >// 'return num / 10 == 0;'> >if>((num>= 0) &&(num<10))> >return> 1;> >else> >return> 0;> }> > // A recursive function to> // find out whether num is> // palindrome or not.> // Initially, dupNum contains> // address of a copy of num.> public> static> int> isPalUtil(>int> num,> >int> dupNum)> {> >// Base case (needed for recursion> >// termination): This statement> >// mainly compares the first digit> >// with the last digit> >if> (oneDigit(num) == 1)> >if>(num == (dupNum) % 10)> >return> 1;> >else> >return> 0;> > >// This is the key line in> >// this method. Note that> >// all recursive calls have> >// a separate copy of num,> >// but they all share same> >// copy of *dupNum. We divide> >// num while moving up the> >// recursion tree> >if> (isPalUtil((>int>)(num / 10), dupNum) == 0)> >return> -1;> > >// The following statements> >// are executed when we move> >// up the recursion call tree> >dupNum = (>int>)(dupNum / 10);> > >// At this point, if num%10> >// contains i'th digit from> >// beginning, then (*dupNum)%10> >// contains i'th digit from end> >if>(num % 10 == (dupNum) % 10)> >return> 1;> >else> >return> 0;> }> > // The main function that uses> // recursive function isPalUtil()> // to find out whether num is> // palindrome or not> public> static> int> isPal(>int> num)> {> >// If num is negative,> >// make it positive> >if> (num <0)> >num = (-num);> > >// Create a separate copy> >// of num, so that modifications> >// made to address dupNum> >// don't change the input number.> >int> dupNum = (num);>// *dupNum = num> > >return> isPalUtil(num, dupNum);> }> > // Driver Code> public> static> void> Main()> {> int> n = 12321;> if>(isPal(n) == 0)> >Console.WriteLine(>'Yes'>);> else> >Console.WriteLine(>'No'>);> > n = 12;> if>(isPal(n) == 0)> >Console.WriteLine(>'Yes'>);> else> >Console.WriteLine(>'No'>);> > n = 88;> if>(isPal(n) == 1)> >Console.WriteLine(>'Yes'>);> else> >Console.WriteLine(>'No'>);> > n = 8999;> if>(isPal(n) == 0)> >Console.WriteLine(>'Yes'>);> else> >Console.WriteLine(>'No'>);> }> }> > // This code is contributed by mits> |
>
>
Javascript
> // A recursive javascript program to> // check whether a given number> // is palindrome or not> > >// A function that returns true> >// only if num contains one digit> >function> oneDigit(num) {> > >if> ((num>= 0) && (num<10))> >return> 1;> >else> >return> 0;> >}> > >function> isPalUtil> >(num , dupNum) {> > >// base condition to return once we> >// move past first digit> >if> (num == 0) {> >return> dupNum;> >}>else> {> >dupNum = isPalUtil(parseInt(num / 10), dupNum);> >}> > >// Check for equality of first digit of> >// num and dupNum> >if> (num % 10 == dupNum % 10) {> >// if first digit values of num and> >// dupNum are equal divide dupNum> >// value by 10 to keep moving in sync> >// with num.> >return> parseInt(dupNum / 10);> >}>else> {> >// At position values are not> >// matching throw exception and exit.> >// no need to proceed further.> >throw> e;> >}> > >}> > >function> isPal(num)> >{> > >if> (num <0)> >num = (-num);> > >var> dupNum = (num);> > >return> isPalUtil(num, dupNum);> >}> > > > >var> n = 1242;> >try> {> >isPal(n);> >document.write(>' Yes'>);> >}>catch> (e) {> >document.write(>' No'>);> >}> >n = 1231;> >try> {> >isPal(n);> >document.write(>' Yes'>);> >}>catch> (e) {> >document.write(>' No'>);> >}> > >n = 12;> >try> {> >isPal(n);> >document.write(>' Yes'>);> >}>catch> (e) {> >document.write(>' No'>);> >}> > >n = 88;> >try> {> >isPal(n);> >document.write(>' Yes'>);> >}>catch> (e) {> >document.write(>' No'>);> >}> > >n = 8999;> >try> {> >isPal(n);> >document.write(>' Yes'>);> >}>catch> (e) {> >document.write(>' No'>);> >}> > // This code is contributed by Amit Katiyar> > |
>
>
PHP
semi contro spore
// A recursive PHP program to // check whether a given number // is palindrome or not // A function that returns true // only if num contains one digit function oneDigit($num) { // comparison operation is faster // than division operation. So // using following instead of // 'return num / 10 == 0;' return (($num>= 0) && ($num<10)); } // A recursive function to find // out whether num is palindrome // or not. Initially, dupNum // contains address of a copy of num. function isPalUtil($num, $dupNum) { // Base case (needed for recursion // termination): This statement // mainly compares the first digit // with the last digit if (oneDigit($num)) return ($num == ($dupNum) % 10); // This is the key line in this // method. Note that all recursive // calls have a separate copy of // num, but they all share same // copy of *dupNum. We divide num // while moving up the recursion tree if (!isPalUtil((int)($num / 10), $dupNum)) return -1; // The following statements are // executed when we move up the // recursion call tree $dupNum = (int)($dupNum / 10); // At this point, if num%10 // contains i'th digit from // beginning, then (*dupNum)%10 // contains i'th digit from end return ($num % 10 == ($dupNum) % 10); } // The main function that uses // recursive function isPalUtil() // to find out whether num is // palindrome or not function isPal($num) { // If num is negative, // make it positive if ($num <0) $num = (-$num); // Create a separate copy of // num, so that modifications // made to address dupNum // don't change the input number. $dupNum = ($num); // *dupNum = num return isPalUtil($num, $dupNum); } // Driver Code $n = 12321; if(isPal($n) == 0) echo 'Yes
'; else echo 'No
'; $n = 12; if(isPal($n) == 0) echo 'Yes
'; else echo 'No
'; $n = 88; if(isPal($n) == 1) echo 'Yes
'; else echo 'No
'; $n = 8999; if(isPal($n) == 0) echo 'Yes
'; else echo 'No
'; // This code is contributed by m_kit ?>> |
>
>Produzione
Yes No Yes No>
Complessità temporale: O(log n)
Spazio ausiliario: O(log n)
Per verificare che un numero sia palindromo o meno senza utilizzare spazio aggiuntivo
Metodo 2: utilizzo del metodo string()
- Quando il numero di cifre di quel numero supera 1018, non possiamo prendere quel numero come intero poiché l'intervallo di long long int non soddisfa il numero specificato.
- Quindi prendi l'input come una stringa, esegui un ciclo dall'inizio a lunghezza/2 e controlla il primo carattere (numerico) fino all'ultimo carattere della stringa e dal penultimo al penultimo, e così via.... Se qualche carattere non corrisponde, la stringa non sarebbe un palindromo.
Di seguito è riportata l'implementazione dell'approccio di cui sopra
C++14
// C++ implementation of the above approach> #include> using> namespace> std;> > // Function to check palindrome> int> checkPalindrome(string str)> {> >// Calculating string length> >int> len = str.length();> > >// Traversing through the string> >// upto half its length> >for> (>int> i = 0; i // Comparing i th character // from starting and len-i // th character from end if (str[i] != str[len - i - 1]) return false; } // If the above loop doesn't return then it is // palindrome return true; } // Driver Code int main() { // taking number as string string st = '112233445566778899000000998877665544332211'; if (checkPalindrome(st) == true) cout << 'Yes'; else cout << 'No'; return 0; } // this code is written by vikkycirus> |
>
>
Giava
// Java implementation of the above approach> import> java.io.*;> > class> GFG{> > // Function to check palindrome> static> boolean> checkPalindrome(String str)> {> > >// Calculating string length> >int> len = str.length();> > >// Traversing through the string> >// upto half its length> >for>(>int> i =>0>; i 2; i++) { // Comparing i th character // from starting and len-i // th character from end if (str.charAt(i) != str.charAt(len - i - 1)) return false; } // If the above loop doesn't return then // it is palindrome return true; } // Driver Code public static void main(String[] args) { // Taking number as string String st = '112233445566778899000000998877665544332211'; if (checkPalindrome(st) == true) System.out.print('Yes'); else System.out.print('No'); } } // This code is contributed by subhammahato348> |
>
>
Python3
# Python3 implementation of the above approach> > # function to check palindrome> def> checkPalindrome(>str>):> > ># Run loop from 0 to len/2> >for> i>in> range>(>0>,>len>(>str>)>/>/>2>):> >if> str>[i] !>=> str>[>len>(>str>)>->i>->1>]:> >return> False> > ># If the above loop doesn't> >#return then it is palindrome> >return> True> > > # Driver code> st>=> '112233445566778899000000998877665544332211'> if>(checkPalindrome(st)>=>=> True>):> >print>(>'it is a palindrome'>)> else>:> >print>(>'It is not a palindrome'>)> |
>
>
C#
// C# implementation of the above approach> using> System;> > class> GFG{> > // Function to check palindrome> static> bool> checkPalindrome(>string> str)> {> > >// Calculating string length> >int> len = str.Length;> > >// Traversing through the string> >// upto half its length> >for>(>int> i = 0; i { // Comparing i th character // from starting and len-i // th character from end if (str[i] != str[len - i - 1]) return false; } // If the above loop doesn't return then // it is palindrome return true; } // Driver Code public static void Main() { // Taking number as string string st = '112233445566778899000000998877665544332211'; if (checkPalindrome(st) == true) Console.Write('Yes'); else Console.Write('No'); } } // This code is contributed by subhammahato348> |
>
>
Javascript
> > // Javascript implementation of the above approach> > // Function to check palindrome> function> checkPalindrome(str)> {> >// Calculating string length> >var> len = str.length;> > >// Traversing through the string> >// upto half its length> >for> (>var> i = 0; i // Comparing ith character // from starting and len-ith // character from end if (str[i] != str[len - i - 1]) return false; } // If the above loop doesn't return then it is // palindrome return true; } // Driver Code // taking number as string let st = '112233445566778899000000998877665544332211'; if (checkPalindrome(st) == true) document.write('Yes'); else document.write('No'); // This code is contributed by Mayank Tyagi> |
>
>Produzione
Yes>
Complessità temporale: O(|str|)
Spazio ausiliario : O(1)
Metodo 3:
Ecco l'approccio più semplice per verificare se un numero è palindromo o meno. Questo approccio può essere utilizzato quando il numero di cifre nel numero specificato è inferiore a 10^18 perché se il numero di cifre di quel numero supera 10^18, non possiamo prendere quel numero come intero poiché l'intervallo di long long int non soddisfa il numero specificato.
Per verificare se il numero dato è palindromo o meno, invertiremo semplicemente le cifre del numero dato e controlleremo se il contrario di quel numero è uguale al numero originale o meno. Se il contrario del numero è uguale a quel numero, il numero sarà palindromo, altrimenti non sarà palindromo.
C++
// C++ program to check if a number is Palindrome> #include> using> namespace> std;> // Function to check Palindrome> bool> checkPalindrome(>int> n)> {> >int> reverse = 0;> >int> temp = n;> >while> (temp != 0) {> >reverse = (reverse * 10) + (temp % 10);> >temp = temp / 10;> >}> >return> (reverse> >== n);>// if it is true then it will return 1;> >// else if false it will return 0;> }> int> main()> {> >int> n = 7007;> >if> (checkPalindrome(n) == 1) {> >cout <<>'Yes
'>;> >}> >else> {> >cout <<>'No
'>;> >}> >return> 0;> }> // This code is contributed by Suruchi Kumari> |
>
>
Giava
/*package whatever //do not write package name here */> > import> java.io.*;> > class> GFG {> >// Java program to check if a number is Palindrome> > >// Function to check Palindrome> >static> boolean> checkPalindrome(>int> n)> >{> >int> reverse =>0>;> >int> temp = n;> >while> (temp !=>0>) {> >reverse = (reverse *>10>) + (temp %>10>);> >temp = temp />10>;> >}> >return> (reverse == n);>// if it is true then it will return 1;> >// else if false it will return 0;> >}> > >// Driver Code> >public> static> void> main(String args[])> >{> >int> n =>7007>;> >if> (checkPalindrome(n) ==>true>) {> >System.out.println(>'Yes'>);> >}> >else> {> >System.out.println(>'No'>);> >}> >}> }> > // This code is contributed by shinjanpatra> |
>
>
Python3
# Python3 program to check if a number is Palindrome> > # Function to check Palindrome> def> checkPalindrome(n):> > >reverse>=> 0> >temp>=> n> >while> (temp !>=> 0>):> >reverse>=> (reverse>*> 10>)>+> (temp>%> 10>)> >temp>=> temp>/>/> 10> > >return> (reverse>=>=> n)># if it is true then it will return 1;> ># else if false it will return 0;> > # driver code> n>=> 7007> if> (checkPalindrome(n)>=>=> 1>):> >print>(>'Yes'>)> > else>:> >print>(>'No'>)> > # This code is contributed by shinjanpatra> |
>
>
C#
// C# program to check if a number is Palindrome> > using> System;> > class> GFG {> > >// Function to check Palindrome> >static> bool> checkPalindrome(>int> n)> >{> >int> reverse = 0;> >int> temp = n;> >while> (temp != 0) {> >reverse = (reverse * 10) + (temp % 10);> >temp = temp / 10;> >}> >return> (> >reverse> >== n);>// if it is true then it will return 1;> >// else if false it will return 0;> >}> > >// Driver Code> >public> static> void> Main(>string>[] args)> >{> >int> n = 7007;> >if> (checkPalindrome(n) ==>true>) {> >Console.WriteLine(>'Yes'>);> >}> >else> {> >Console.WriteLine(>'No'>);> >}> >}> }> > // This code is contributed by phasing17> |
>
>
Javascript
> > // JavaScript program to check if a number is Palindrome> > // Function to check Palindrome> function> checkPalindrome(n)> {> >let reverse = 0;> >let temp = n;> >while> (temp != 0) {> >reverse = (reverse * 10) + (temp % 10);> >temp = Math.floor(temp / 10);> >}> >return> (reverse == n);>// if it is true then it will return 1;> >// else if false it will return 0;> }> > // driver code> > let n = 7007;> if> (checkPalindrome(n) == 1) {> >document.write(>'Yes'>,>''>);> }> else> {> >document.write(>'No'>,>''>);> }> > > // This code is contributed by shinjanpatra> > > |
>
>Produzione
Yes>
Complessità temporale: O(log10(n)) o O(Numero di cifre in un dato numero)
Spazio ausiliario : O(1) o costante
Questo articolo è compilato daAshish Barnwal.