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 

Approach:

  1. 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
  2. Return ans.

Below is the implementation of the above approach:

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// 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;
}
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// 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
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# 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
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// 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)
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<?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.
?>
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Output:
2

Time Complexity: O(N * M).

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