Leetcode - Longest Common String

Given two strings ‘X’ and ‘Y’, find the length of the longest common substring.

For example, if the given strings are “GeeksforGeeks” and “GeeksQuiz”, the output should be 5 as longest common substring is “Geeks”

这道题目不是Leetcode 上的。一开始觉得很难，看了答案后发现dp做简单。
dp就是这样，想不到，觉得这道题目太变态了，想到了，觉得好简单。
但是，往往想到，都是建立在，看了答案基础上的。
平常心。

My code:

public int longestCommonString(String s1, String s2) {
        if (s1 == null || s1.length() == 0)
            return 0;
        if (s2 == null || s2.length() == 0)
            return 0;
        
        int[][] dp = new int[s1.length()][s2.length()];
        int max = Integer.MIN_VALUE;
        for (int i = 0; i < s1.length(); i++) {
            if (s2.charAt(0) == s1.charAt(i)) {
                dp[i][0] = 1;
                max = 1;
            }
        }
        for (int i = 0; i < s2.length(); i++) {
            if (s1.charAt(0) == s2.charAt(i)) {
                dp[0][i] = 1;
                max = 1;
            }
        }
        
        for (int i = 1; i < s1.length(); i++) {
            for (int j = 1; j < s2.length(); j++) {
                if (s1.charAt(i) == s2.charAt(j))
                    dp[i][j] = dp[i - 1][j - 1] + 1;
                max = Math.max(max, dp[i][j]);
            }
        }
        
        return max;
    }

就是建立一个dp[][] 数组用来记录 i, j 结尾的最长尾字符串长度。
然后一步步递推。
参考网页：
http://www.geeksforgeeks.org/longest-common-substring/

Anyway, Good luck, Richardo！