Minimum changes required to make first string substring of second string

Given two strings S1 and S2 ( size of S1 <= Size of S2 ). The task is to find the minimum number of characters to be replaced in the string S2, such that the string S1 is a substring of S2.

Examples:

Input : S1 = cdef, S2 = abbdef
Output : 1

Input : S1 = gfg, S2 = fgg
Output : 2

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:

Traverse the string S2
- From every index in S2, check the number of mis-matching characters in substring of length of S1
- Store and update the minimum of prev and current mis-match in ans
Return ans.

Below is the implementation of the above approach:

C++

// CPP program to find the minimum number of 
// characters to be replaced in string S2, such 
// that S1 is a substring of S2 
  
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to find the minimum number of 
// characters to be replaced in string S2, such 
// that S1 is a substring of S2 
int minimumChar(string S1, string S2) 
{ 
    // Get the sizes of both strings 
    int n = S1.size(), m = S2.size(); 
  
    int ans = INT_MAX; 
  
    // Traverse the string S2 
    for (int i = 0; i < m - n + 1; i++) { 
        int minRemovedChar = 0; 
  
        // From every index in S2, check the number of 
        // mis-matching characters in substring of 
        // length of S1 
        for (int j = 0; j < n; j++) { 
            if (S1[j] != S2[i + j]) { 
                minRemovedChar++; 
            } 
        } 
  
        // Take minimum of prev and current mis-match 
        ans = min(minRemovedChar, ans); 
    } 
  
    // return answer 
    return ans; 
} 
  
// Driver Code 
int main() 
{ 
    string S1 = "abc"; 
    string S2 = "paxzk"; 
  
    cout << minimumChar(S1, S2); 
  
    return 0; 
} 

Java

// Java program to find the minimum  
// number of characters to be  
// replaced in string S2, such 
// that S1 is a substring of S2 
import java.io.*; 
  
class GFG  
{ 
  
// Function to find the minimum  
// number of characters to be  
// replaced in string S2, such 
// that S1 is a substring of S2 
static int minimumChar(String S1, 
                       String S2) 
{ 
    // Get the sizes of both strings 
    int n = S1.length(); 
    int m = S2.length(); 
  
    int ans = Integer.MAX_VALUE ; 
  
    // Traverse the string S2 
    for (int i = 0; i < m - n + 1; i++) 
    { 
        int minRemovedChar = 0; 
  
        // From every index in S2, check  
        // the number of mis-matching  
        // characters in substring of 
        // length of S1 
        for (int j = 0; j < n; j++)  
        { 
            if (S1.charAt(j) != S2.charAt(i + j))  
            { 
                minRemovedChar++; 
            } 
        } 
  
        // Take minimum of prev and  
        // current mis-match 
        ans = Math.min(minRemovedChar, ans); 
    } 
  
    // return answer 
    return ans; 
} 
  
// Driver Code 
public static void main (String[] args)  
{ 
    String S1 = "abc"; 
    String S2 = "paxzk"; 
      
    System.out.println(minimumChar(S1, S2)); 
} 
} 
  
// This code is contributed by Shashank 

Python3

# Python3 program to find the minimum  
# number of characters to be replaced  
# in string S2, such that S1 is a  
# substring of S2 
import sys  
  
# Function to find the minimum number of 
# characters to be replaced in string S2, 
# such that S1 is a substring of S2 
def minimumChar(S1, S2): 
      
    # Get the sizes of both strings 
    n, m = len(S1), len(S2) 
  
    ans = sys.maxsize 
  
    # Traverse the string S2 
    for i in range(m - n + 1): 
        minRemovedChar = 0
  
        # From every index in S2, check the  
        # number of mis-matching characters  
        # in substring of length of S1 
        for j in range(n): 
            if (S1[j] != S2[i + j]): 
                minRemovedChar += 1
                  
        # Take minimum of prev and  
        # current mis-match 
        ans = min(minRemovedChar, ans) 
          
    # return answer 
    return ans 
      
# Driver Code 
if __name__ == '__main__': 
    S1 = "abc"
    S2 = "paxzk"
    print(minimumChar(S1, S2)) 
  
# This code is contributed  
# by PrinciRaj1992 

C#

// C# program to find the minimum  
// number of characters to be  
// replaced in string S2, such 
// that S1 is a substring of S2 
using System; 
  
class GFG  
{ 
  
// Function to find the minimum  
// number of characters to be  
// replaced in string S2, such 
// that S1 is a substring of S2 
static int minimumChar(String S1, 
                       String S2) 
{ 
    // Get the sizes of both strings 
    int n = S1.Length; 
    int m = S2.Length; 
  
    int ans = Int32.MaxValue ; 
  
    // Traverse the string S2 
    for (int i = 0; i < m - n + 1; i++) 
    { 
        int minRemovedChar = 0; 
  
        // From every index in S2, check  
        // the number of mis-matching  
        // characters in substring of 
        // length of S1 
        for (int j = 0; j < n; j++)  
        { 
            if (S1[j] != S2[i + j])  
            { 
                minRemovedChar++; 
            } 
        } 
  
        // Take minimum of prev and  
        // current mis-match 
        ans = Math.Min(minRemovedChar, ans); 
    } 
  
    // return answer 
    return ans; 
} 
  
// Driver Code 
public static void Main()  
{ 
    String S1 = "abc"; 
    String S2 = "paxzk"; 
      
    Console.WriteLine(minimumChar(S1, S2)); 
} 
} 
  
// This code is contributed  
// by Akanksha Rai(Abby_akku) 

PHP

<?php 
// PHP program to find the minimum  
// number of characters to be replaced  
// in string S2, such that S1 is a  
// substring of S2  
  
// Function to find the minimum number  
// of characters to be replaced in  
// string S2, such that S1 is a  
// substring of S2  
function minimumChar($S1, $S2)  
{  
    // Get the sizes of both strings  
    $n = strlen($S1); 
    $m = strlen($S2);  
  
    $ans = PHP_INT_MAX;  
  
    // Traverse the string S2  
    for ($i = 0; $i < $m - $n + 1; $i++)  
    {  
        $minRemovedChar = 0;  
  
        // From every index in S2, check  
        // the number of mis-matching  
        // characters in substring of  
        // length of S1  
        for ($j = 0; $j < $n; $j++)  
        {  
            if ($S1[$j] != $S2[$i + $j])  
            {  
                $minRemovedChar++;  
            }  
        }  
  
        // Take minimum of prev and  
        // current mis-match  
        $ans = min($minRemovedChar, $ans);  
    }  
  
    // return answer  
    return $ans;  
}  
  
// Driver Code  
$S1 = "abc";  
$S2 = "paxzk";  
  
echo minimumChar($S1, $S2);  
  
// This code is contributed by ajit. 
?> 

Output:

Time Complexity: O(N * M).

My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python3

C#

PHP

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