Longest Common Substring

class Solution {
    public int longestCommonSubstr(String str1, String str2) {
        int n = str1.length();
        int m = str2.length();

        int[][] dp = new int[n + 1][m + 1];

        int ans = 0;

        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= m; j++) {
                if (str1.charAt(i - 1) == str2.charAt(j - 1)) {
                    dp[i][j] = 1 + dp[i - 1][j - 1];
                    ans = Math.max(ans, dp[i][j]);
                } else
                    dp[i][j] = 0;
            }
        }

        return ans;
    }
}