Given two strings, find the longest common subsequence (LCS).

Your code should return the length of LCS.

Have you met this question in a real interview? Yes
Clarification
What‘s the definition of Longest Common Subsequence?

https://en.wikipedia.org/wiki/Longest_common_subsequence_problem
http://baike.baidu.com/view/2020307.htm
Example
For "ABCD" and "EDCA", the LCS is "A" (or "D", "C"), return 1.

For "ABCD" and "EACB", the LCS is "AC", return 2.

 public int longestCommonSubsequence(String A, String B) {
        // write your code here
        //state 
        int m = A.length(), n = B.length();
        if (m == 0 || n == 0 || A == null || B == null) {
            return 0;
        }
        int[][] res = new int[m + 1][n + 1];
        
        //initialize
        for (int i = 0; i <= m; i++) {
            res[i][0] = 0;
        }
         for (int i = 0; i <= n; i++) {
            res[0][i] = 0;
        }
        //function
        for (int i = 1; i <= m; i++) {
            for (int j = 1; j <= n; j++) {
                if (A.charAt(i - 1) == B.charAt(j - 1)) {
                    res[i][j] = res[i - 1][j - 1] + 1;
                } else {
                    res[i][j] = Math.max(res[i - 1][j], res[i][j - 1]);
                }
            }
        }
        return res[m][n];
        
    }