Given an input string and a pattern check if characters in the input string follows the same order as determined by characters present in the pattern. Supponiamo che non ci saranno caratteri duplicati nel modello.
Esempi:
Input: string = 'engineers rock' pattern = 'er'; Output: true All 'e' in the input string are before all 'r'. Input: string = 'engineers rock' pattern = 'egr'; Output: false There are two 'e' after 'g' in the input string. Input: string = 'engineers rock' pattern = 'gsr'; Output: false There are one 'r' before 's' in the input string.
Abbiamo discusso due approcci per risolvere questo problema.
Controlla se la stringa segue l'ordine dei caratteri definito da un modello oppure no | Insieme 1
Controlla se la stringa segue l'ordine dei caratteri definito da un modello oppure no | Insieme 2
In questo approccio assegniamo innanzitutto un'etichetta (o un ordine) ai caratteri del pattern. Le etichette vengono assegnate in ordine crescente.
Ad esempio, il modello "gsr" è etichettato come segue
'g' => 1 's' => 2 'r' => 3
Significa che verrà prima la "g", poi la "s" e poi la "r"
Dopo aver assegnato le etichette ai caratteri del modello, iteriamo attraverso i caratteri della stringa. Durante l'attraversamento teniamo traccia dell'etichetta (o dell'ordine) dell'ultimo carattere visitato. Se l'etichetta del carattere corrente è inferiore al carattere precedente, restituiamo false. Altrimenti aggiorniamo l'ultima etichetta. Se tutti i caratteri seguono l'ordine restituiamo true.
Di seguito è riportata l'implementazione
C++// C++ program to find if a string follows order // defined by a given pattern. #include
// Java program to find if a string follows order // defined by a given pattern. class GFG { static int CHAR_SIZE = 256; // Returns true if characters of str follow // order defined by a given ptr. static boolean checkPattern(String str String pat) { int[] label = new int[CHAR_SIZE]; // Initialize all orders as -1 for (int i = 0; i < CHAR_SIZE; i++) label[i] = -1; // Assign an order to pattern characters // according to their appearance in pattern int order = 1; for (int i = 0; i < pat.length(); i++) { // give the pattern characters order label[pat.charAt(i)] = order; // increment the order order++; } // Now one by check if string characters // follow above order int last_order = -1; for (int i = 0; i < str.length(); i++) { if (label[str.charAt(i)] != -1) { // If order of this character is less // than order of previous return false. if (label[str.charAt(i)] < last_order) return false; // Update last_order for next iteration last_order = label[str.charAt(i)]; } } // return that str followed pat return true; } // Driver code public static void main(String[] args) { String str = 'engineers rock'; String pattern = 'gsr'; System.out.println(checkPattern(str pattern)); } } // This code is contributed by // sanjeev2552
# Python3 program to find if a string follows # order defined by a given pattern CHAR_SIZE = 256 # Returns true if characters of str follow # order defined by a given ptr. def checkPattern(Str pat): # Initialize all orders as -1 label = [-1] * CHAR_SIZE # Assign an order to pattern characters # according to their appearance in pattern order = 1 for i in range(len(pat)): # Give the pattern characters order label[ord(pat[i])] = order # Increment the order order += 1 # Now one by one check if string # characters follow above order last_order = -1 for i in range(len(Str)): if (label[ord(Str[i])] != -1): # If order of this character is less # than order of previous return false if (label[ord(Str[i])] < last_order): return False # Update last_order for next iteration last_order = label[ord(Str[i])] # return that str followed pat return True # Driver Code if __name__ == '__main__': Str = 'engineers rock' pattern = 'gsr' print(checkPattern(Str pattern)) # This code is contributed by himanshu77
// C# program to find if a string follows order // defined by a given pattern. using System; class GFG { static int CHAR_SIZE = 256; // Returns true if characters of str follow // order defined by a given ptr. static bool checkPattern(String str String pat) { int[] label = new int[CHAR_SIZE]; // Initialize all orders as -1 for (int i = 0; i < CHAR_SIZE; i++) label[i] = -1; // Assign an order to pattern characters // according to their appearance in pattern int order = 1; for (int i = 0; i < pat.Length; i++) { // give the pattern characters order label[pat[i]] = order; // increment the order order++; } // Now one by check if string characters // follow above order int last_order = -1; for (int i = 0; i < str.Length; i++) { if (label[str[i]] != -1) { // If order of this character is less // than order of previous return false. if (label[str[i]] < last_order) return false; // Update last_order for next iteration last_order = label[str[i]]; } } // return that str followed pat return true; } // Driver code public static void Main(String[] args) { String str = 'engineers rock'; String pattern = 'gsr'; Console.WriteLine(checkPattern(str pattern)); } } // This code is contributed by 29AjayKumar
<script> // Javascript program to find if a string follows order // defined by a given pattern. let CHAR_SIZE = 256; // Returns true if characters of str follow // order defined by a given ptr. function checkPattern(strpat) { let label = new Array(CHAR_SIZE); // Initialize all orders as -1 for (let i = 0; i < CHAR_SIZE; i++) label[i] = -1; // Assign an order to pattern characters // according to their appearance in pattern let order = 1; for (let i = 0; i < pat.length; i++) { // give the pattern characters order label[pat[i].charCodeAt(0)] = order; // increment the order order++; } // Now one by check if string characters // follow above order let last_order = -1; for (let i = 0; i < str.length; i++) { if (label[str[i].charCodeAt(0)] != -1) { // If order of this character is less // than order of previous return false. if (label[str[i].charCodeAt(0)] < last_order) return false; // Update last_order for next iteration last_order = label[str[i].charCodeAt(0)]; } } // return that str followed pat return true; } // Driver code let str = 'engineers rock'; let pattern = 'gsr'; document.write(checkPattern(str pattern)); // This code is contributed by rag2127 </script>
Produzione
false
Complessità temporale di questo programma è SU) con spazio aggiuntivo costante (l'etichetta dell'array ha dimensione costante 256).
Spazio ausiliario: O(256).