Given two strings str of length N and word of length M, the task is to remove all the occurrences of the string word from the string str.
Examples:
Input: str = “asmGeeksasmasmForasmGeeks”, word = “asm”
Output: GeeksForGeeks
Explanation:
Removing “asm” from the string, str modifies str to GeeksForGeeksInput: str = “Z-kmalgorithmkmiskmkmkmhelpfulkminkmsearching”, word = “km”
Output: Z-algorithmishelpfulinsearchingExplanation:
Removing “km” from the string, str modifies str to “Z-algorithmishelpfulinsearching”.
Naive Approach: The simplest approach to solve this problem is to iterate over the characters of the string str. For every index, check if a substring can be found whose starting index is equal to the current index and the substring is equal to the string, word. If found to be true, then remove the substring. Finally, print the string.
Time Complexity: O(N2)
Auxiliary Space: O(1)
STL-based Approach: Remove all the occurrence of the string word from the string str using replace() method.
Time Complexity: O(N2)
Auxiliary Space: O(1)
Efficient Approach: The above approach can be optimized using Z-algorithm. Follow the steps below to solve the problem:
- Initialize a string, say res, to store the string by removing the words from the given string str.
- Initialize an array, say Z[], to store the Z-value of the string.
- Find all occurrences of the string word in the given string str using Z-algorithm.
- Finally, traverse the array Z[] and check if z[i + length(word) + 1] is equal to length(word) or not. If found to be true, then update i += length(word) – 1.
- Otherwise, append current character into the string res.
Below is the implementation of the above approach:
C++
// C++ program for the above approach#include <bits/stdc++.h>using namespace std;// Function to fill the Z-array for strvoid getZarr(string str, int Z[]){ int n = str.length(); int k; // L Stores start index of window // which matches with prefix of str int L = 0; // R Stores end index of window // which matches with prefix of str int R = 0; // Iterate over the characters of str for (int i = 1; i < n; ++i) { // If i is greater than R if (i > R) { // Update L and R L = R = i; // If substring match with prefix while (R < n && str[R - L] == str[R]) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } else { // Update k k = i - L; // if Z[k] is less than // remaining interval if (Z[k] < R - i + 1) { // Update Z[i] Z[i] = Z[k]; } else { // Start from R and check manually L = i; while (R < n && str[R - L] == str[R]) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } } }}// Function to remove all the occurrences// of word from strstring goodStr(string str, string word){ // Create concatenated string "P$T" string concat = word + "$" + str; int l = concat.length(); // Store Z array of concat int Z[l]; getZarr(concat, Z); // Stores string, str by removing all // the occurrences of word from str string res; // Stores length of word int pSize = word.size(); // Traverse the array, Z[] for (int i = 0; i < l; ++i) { // if Z[i + pSize + 1] equal to // length of word if (i + pSize < l - 1 && Z[i + pSize + 1] == pSize) { // Update i i += pSize - 1; } else if (i < str.length()) { res += str[i]; } } return res;}// Driver Codeint main(){ string str = "Z-kmalgorithmkmiskmkmkmhelpfulkminkmsearching"; string word = "km"; cout << goodStr(str, word); return 0;} |
Java
// Java program for the above approachimport java.util.*;class GFG{ // Function to fill the Z-array for str static void getZarr(String str, int Z[]) { int n = str.length(); int k; // L Stores start index of window // which matches with prefix of str int L = 0; // R Stores end index of window // which matches with prefix of str int R = 0; // Iterate over the characters of str for (int i = 1; i < n; ++i) { // If i is greater than R if (i > R) { // Update L and R L = R = i; // If subString match with prefix while (R < n && str.charAt(R - L) == str.charAt(R)) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } else { // Update k k = i - L; // if Z[k] is less than // remaining interval if (Z[k] < R - i + 1) { // Update Z[i] Z[i] = Z[k]; } else { // Start from R and check manually L = i; while (R < n && str.charAt(R - L) == str.charAt(R)) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } } } } // Function to remove all the occurrences // of word from str static String goodStr(String str, String word) { // Create concatenated String "P$T" String concat = word + "$" + str; int l = concat.length(); // Store Z array of concat int []Z = new int[l]; getZarr(concat, Z); // Stores String, str by removing all // the occurrences of word from str String res=""; // Stores length of word int pSize = word.length(); // Traverse the array, Z[] for (int i = 0; i < l; ++i) { // if Z[i + pSize + 1] equal to // length of word if (i + pSize < l - 1 && Z[i + pSize + 1] == pSize) { // Update i i += pSize - 1; } else if (i < str.length()) { res += str.charAt(i); } } return res; } // Driver Code public static void main(String[] args) { String str = "Z-kmalgorithmkmiskmkmkmhelpfulkminkmsearching"; String word = "km"; System.out.print(goodStr(str, word)); }}// This code is contributed by 29AjayKumar |
Python3
# Python 3 program for the above approach# Function to fill the Z-array for strdef getZarr(st, Z): n = len(st) k = 0 # L Stores start index of window # which matches with prefix of str L = 0 # R Stores end index of window # which matches with prefix of str R = 0 # Iterate over the characters of str for i in range(1, n): # If i is greater than R if (i > R): # Update L and R L = R = i # If substring match with prefix while (R < n and st[R - L] == st[R]): # Update R R += 1 # Update Z[i] Z[i] = R - L # Update R R -= 1 else: # Update k k = i - L # if Z[k] is less than # remaining interval if (Z[k] < R - i + 1): # Update Z[i] Z[i] = Z[k] else: # Start from R and check manually L = i while (R < n and st[R - L] == st[R]): # Update R R += 1 # Update Z[i] Z[i] = R - L # Update R R -= 1# Function to remove all the occurrences# of word from strdef goodStr(st, word): # Create concatenated string "P$T" concat = word + "$" + st l = len(concat) # Store Z array of concat Z = [0]*l getZarr(concat, Z) # Stores string, str by removing all # the occurrences of word from str res = "" # Stores length of word pSize = len(word) # Traverse the array, Z[] for i in range(l): # if Z[i + pSize + 1] equal to # length of word if (i + pSize < l - 1 and Z[i + pSize + 1] == pSize): # Update i i += pSize - 1 elif (i < len(st)): res += st[i] return res# Driver Codeif __name__ == "__main__": st = "Z-kmalgorithmkmiskmkmkmhelpfulkminkmsearching" word = "km" print(goodStr(st, word)) # This code is contributed by chitranayal. |
C#
// C# program for the above approachusing System;using System.Collections.Generic;public class GFG{ // Function to fill the Z-array for str static void getZarr(string str, int[] Z) { int n = str.Length; int k; // L Stores start index of window // which matches with prefix of str int L = 0; // R Stores end index of window // which matches with prefix of str int R = 0; // Iterate over the characters of str for (int i = 1; i < n; ++i) { // If i is greater than R if (i > R) { // Update L and R L = R = i; // If subString match with prefix while (R < n && str[R - L] == str[R]) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } else { // Update k k = i - L; // if Z[k] is less than // remaining interval if (Z[k] < R - i + 1) { // Update Z[i] Z[i] = Z[k]; } else { // Start from R and check manually L = i; while (R < n && str[R - L] == str[R]) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } } } } // Function to remove all the occurrences // of word from str static string goodStr(string str, string word) { // Create concatenated String "P$T" string concat = word + "$" + str; int l = concat.Length; // Store Z array of concat int []Z = new int[l]; getZarr(concat, Z); // Stores String, str by removing all // the occurrences of word from str string res=""; // Stores length of word int pSize = word.Length; // Traverse the array, Z[] for (int i = 0; i < l; ++i) { // if Z[i + pSize + 1] equal to // length of word if (i + pSize < l - 1 && Z[i + pSize + 1] == pSize) { // Update i i += pSize - 1; } else if (i < str.Length) { res += str[i]; } } return res; } // Driver Code static public void Main() { string str = "Z-kmalgorithmkmiskmkmkmhelpfulkminkmsearching"; string word = "km"; Console.WriteLine(goodStr(str, word)); }}// This code is contributed by sanjoy_62. |
Javascript
<script>//js program for the above approach// Function to fill the Z-array for strfunction getZarr(str,Z){ let n = str.length; let k; // L Stores start index of window // which matches with prefix of str let L = 0; // R Stores end index of window // which matches with prefix of str let R = 0; // Iterate over the characters of str for (let i = 1; i < n; ++i) { // If i is greater than R if (i > R) { // Update L and R L = R = i; // If subString match with prefix while (R < n && str[R - L] == str[R]) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } else { // Update k k = i - L; // if Z[k] is less than // remaining interval if (Z[k] < R - i + 1) { // Update Z[i] Z[i] = Z[k]; } else { // Start from R and check manually L = i; while (R < n && str[R - L] == str[R]) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } } }}// Function to remove all the occurrences// of word from strfunction goodStr(str,word){ // Create concatenated String "P$T" let concat = word + "$" + str; let l = concat.length; // Store Z array of concat let Z = new Array(l); getZarr(concat, Z); // Stores String, str by removing all // the occurrences of word from str let res=""; // Stores length of word let pSize = word.length; // Traverse the array, Z[] for (let i = 0; i < l; ++i) { // if Z[i + pSize + 1] equal to // length of word if (i + pSize < l - 1 && Z[i + pSize + 1] == pSize) { // Update i i += pSize - 1; } else if (i < str.length) { res += str[i]; } } return res;}// Driver Codelet str = "Z-kmalgorithmkmiskmkmkmhelpfulkminkmsearching";let word = "km";document.write(goodStr(str, word));</script> |
C++
// C++ program for the above approach#include <bits/stdc++.h>using namespace std;// Function to fill the Z-array for strvoid getZarr(string str, int Z[]){ int n = str.length(); int k; // L Stores start index of window // which matches with prefix of str int L = 0; // R Stores end index of window // which matches with prefix of str int R = 0; // Iterate over the characters of str for (int i = 1; i < n; ++i) { // If i is greater than R if (i > R) { // Update L and R L = R = i; // If substring match with prefix while (R < n && str[R - L] == str[R]) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } else { // Update k k = i - L; // if Z[k] is less than // remaining interval if (Z[k] < R - i + 1) { // Update Z[i] Z[i] = Z[k]; } else { // Start from R and check manually L = i; while (R < n && str[R - L] == str[R]) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } } }}// Function to remove all the occurrences// of word from strstring goodStr(string str, string word){ // Create concatenated string "P$T" string concat = word + "$" + str; int l = concat.length(); // Store Z array of concat int Z[l]; getZarr(concat, Z); // Stores string, str by removing all // the occurrences of word from str string res; // Stores length of word int pSize = word.size(); // Traverse the array, Z[] for (int i = 0; i < l; ++i) { // if Z[i + pSize + 1] equal to // length of word if (i + pSize < l - 1 && Z[i + pSize + 1] == pSize) { // Update i i += pSize - 1; } else if (i < str.length()) { res += str[i]; } } return res;}// Driver Codeint main(){ string str = "Z-kmalgorithmkmiskmkmkmhelpfulkminkmsearching"; string word = "km"; cout << goodStr(str, word); return 0;} |
Java
// Java program for the above approachimport java.util.*;class GFG{ // Function to fill the Z-array for str static void getZarr(String str, int Z[]) { int n = str.length(); int k; // L Stores start index of window // which matches with prefix of str int L = 0; // R Stores end index of window // which matches with prefix of str int R = 0; // Iterate over the characters of str for (int i = 1; i < n; ++i) { // If i is greater than R if (i > R) { // Update L and R L = R = i; // If subString match with prefix while (R < n && str.charAt(R - L) == str.charAt(R)) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } else { // Update k k = i - L; // if Z[k] is less than // remaining interval if (Z[k] < R - i + 1) { // Update Z[i] Z[i] = Z[k]; } else { // Start from R and check manually L = i; while (R < n && str.charAt(R - L) == str.charAt(R)) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } } } } // Function to remove all the occurrences // of word from str static String goodStr(String str, String word) { // Create concatenated String "P$T" String concat = word + "$" + str; int l = concat.length(); // Store Z array of concat int []Z = new int[l]; getZarr(concat, Z); // Stores String, str by removing all // the occurrences of word from str String res=""; // Stores length of word int pSize = word.length(); // Traverse the array, Z[] for (int i = 0; i < l; ++i) { // if Z[i + pSize + 1] equal to // length of word if (i + pSize < l - 1 && Z[i + pSize + 1] == pSize) { // Update i i += pSize - 1; } else if (i < str.length()) { res += str.charAt(i); } } return res; } // Driver Code public static void main(String[] args) { String str = "Z-kmalgorithmkmiskmkmkmhelpfulkminkmsearching"; String word = "km"; System.out.print(goodStr(str, word)); }}// This code is contributed by 29AjayKumar |
Python3
# Python 3 program for the above approach# Function to fill the Z-array for strdef getZarr(st, Z): n = len(st) k = 0 # L Stores start index of window # which matches with prefix of str L = 0 # R Stores end index of window # which matches with prefix of str R = 0 # Iterate over the characters of str for i in range(1, n): # If i is greater than R if (i > R): # Update L and R L = R = i # If substring match with prefix while (R < n and st[R - L] == st[R]): # Update R R += 1 # Update Z[i] Z[i] = R - L # Update R R -= 1 else: # Update k k = i - L # if Z[k] is less than # remaining interval if (Z[k] < R - i + 1): # Update Z[i] Z[i] = Z[k] else: # Start from R and check manually L = i while (R < n and st[R - L] == st[R]): # Update R R += 1 # Update Z[i] Z[i] = R - L # Update R R -= 1# Function to remove all the occurrences# of word from strdef goodStr(st, word): # Create concatenated string "P$T" concat = word + "$" + st l = len(concat) # Store Z array of concat Z = [0]*l getZarr(concat, Z) # Stores string, str by removing all # the occurrences of word from str res = "" # Stores length of word pSize = len(word) # Traverse the array, Z[] for i in range(l): # if Z[i + pSize + 1] equal to # length of word if (i + pSize < l - 1 and Z[i + pSize + 1] == pSize): # Update i i += pSize - 1 elif (i < len(st)): res += st[i] return res# Driver Codeif __name__ == "__main__": st = "Z-kmalgorithmkmiskmkmkmhelpfulkminkmsearching" word = "km" print(goodStr(st, word)) # This code is contributed by chitranayal. |
C#
// C# program for the above approachusing System;using System.Collections.Generic;public class GFG{ // Function to fill the Z-array for str static void getZarr(string str, int[] Z) { int n = str.Length; int k; // L Stores start index of window // which matches with prefix of str int L = 0; // R Stores end index of window // which matches with prefix of str int R = 0; // Iterate over the characters of str for (int i = 1; i < n; ++i) { // If i is greater than R if (i > R) { // Update L and R L = R = i; // If subString match with prefix while (R < n && str[R - L] == str[R]) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } else { // Update k k = i - L; // if Z[k] is less than // remaining interval if (Z[k] < R - i + 1) { // Update Z[i] Z[i] = Z[k]; } else { // Start from R and check manually L = i; while (R < n && str[R - L] == str[R]) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } } } } // Function to remove all the occurrences // of word from str static string goodStr(string str, string word) { // Create concatenated String "P$T" string concat = word + "$" + str; int l = concat.Length; // Store Z array of concat int []Z = new int[l]; getZarr(concat, Z); // Stores String, str by removing all // the occurrences of word from str string res=""; // Stores length of word int pSize = word.Length; // Traverse the array, Z[] for (int i = 0; i < l; ++i) { // if Z[i + pSize + 1] equal to // length of word if (i + pSize < l - 1 && Z[i + pSize + 1] == pSize) { // Update i i += pSize - 1; } else if (i < str.Length) { res += str[i]; } } return res; } // Driver Code static public void Main() { string str = "Z-kmalgorithmkmiskmkmkmhelpfulkminkmsearching"; string word = "km"; Console.WriteLine(goodStr(str, word)); }}// This code is contributed by sanjoy_62. |
Javascript
<script>//js program for the above approach// Function to fill the Z-array for strfunction getZarr(str,Z){ let n = str.length; let k; // L Stores start index of window // which matches with prefix of str let L = 0; // R Stores end index of window // which matches with prefix of str let R = 0; // Iterate over the characters of str for (let i = 1; i < n; ++i) { // If i is greater than R if (i > R) { // Update L and R L = R = i; // If subString match with prefix while (R < n && str[R - L] == str[R]) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } else { // Update k k = i - L; // if Z[k] is less than // remaining interval if (Z[k] < R - i + 1) { // Update Z[i] Z[i] = Z[k]; } else { // Start from R and check manually L = i; while (R < n && str[R - L] == str[R]) { // Update R R++; } // Update Z[i] Z[i] = R - L; // Update R R--; } } }}// Function to remove all the occurrences// of word from strfunction goodStr(str,word){ // Create concatenated String "P$T" let concat = word + "$" + str; let l = concat.length; // Store Z array of concat let Z = new Array(l); getZarr(concat, Z); // Stores String, str by removing all // the occurrences of word from str let res=""; // Stores length of word let pSize = word.length; // Traverse the array, Z[] for (let i = 0; i < l; ++i) { // if Z[i + pSize + 1] equal to // length of word if (i + pSize < l - 1 && Z[i + pSize + 1] == pSize) { // Update i i += pSize - 1; } else if (i < str.length) { res += str[i]; } } return res;}// Driver Codelet str = "Z-kmalgorithmkmiskmkmkmhelpfulkminkmsearching";let word = "km";document.write(goodStr(str, word));</script> |
Time Complexity: O(N + M)
Auxiliary Space: O(N)
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