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Prashant Mishra
Prashant Mishra

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Length of longest common substring

Given two strings. The task is to find the length of the longest common substring.

Example 1:

Input: S1 = "ABCDGH", S2 = "ACDGHR", n = 6, m = 6
Output: 4
Explanation: The longest common substring
is "CDGH" which has length 4.

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Usual longest common subsequence will require slight modification
because we are trying to find consecutive sequences that are matching.
so, dp[i][j] = 1+ dp[i-1][j-1]; if char at index i and j matches in both the strings.

For more clarity refer this link

//User function Template for Java
class Solution{
    int longestCommonSubstr(String S1, String S2, int n, int m){
         //we will use same approach that we used in longest common subsequence
         //with slight modification
         int dp[][]   = new int[n+1][m+1];// 1 based indexing
         //base cased
         //since its 0 based indexing first row and first column will have 0 values
         //top down approach
         for(int i =0;i<=n;i++){
             dp[i][0] = 0;
         for(int j=0;j<=m;j++){
              dp[0][j] = 0;
         int ans = 0;
         for(int i=1;i<=n;i++){
             for(int j =1;j<=m;j++){
                     dp[i][j] = 1 + dp[i-1][j-1];
                     ans = Integer.max(dp[i][j],ans);
                 else dp[i][j] =0;

         return ans;

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