Longest Common Substring

#include <bits/stdc++.h> 
int lcs(string &str1, string &str2){
	int n = str1.size();
    int m = str2.size();
    vector<vector<int>> dp(n+1, vector<int>(m+1, 0));
    for(int j=0;j<=m;j++) dp[0][j] = 0;
    for(int i=0;i<=n;i++) dp[i][0] = 0;
    int ans = 0;
    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++){
            if(str1[i-1] == str2[j-1]){
                dp[i][j] = 1 + dp[i-1][j-1];
                ans = max(ans, dp[i][j]);
            }
            else dp[i][j] = 0;
        }
    }
    return ans;
}