最长公共子串

public static String lcStr(String s1, String s2) {
        int len1 = s1.length();
        int len2 = s2.length();
        int max = 0;
        //flag 表示最长功能子串起始位置 
        int flag = -1;
        if (len1 == 0 || len2 == 0) {
            return "";
        }
        //为了初始化方便 使用了n+1个空间 result[i][j]表示包含i j两个元素最长公共子串的最长长度
        int[][] result = new int[len1 + 1][len2 + 1];
        for (int i = 0; i < len1; i++) {
            result[i][0] = 0;
        }
        for (int i = 0; i < len2; i++) {
            result[0][i] = 0;
        }
        //显然对于s1(i),s2(j)只有两种情况 
        for (int i = 0; i < len1; i++) {
            for (int j = 0; j < len2; j++) {
                if (s1.charAt(i) == s2.charAt(j)) {
                    result[i + 1][j + 1] = result[i][j] + 1;
                } else {
                    result[i + 1][j + 1] = 0;
                }
                if (max < result[i + 1][j + 1]) {
                    max = result[i + 1][j + 1];
                    flag = i - max + 1;
                }
            }
        }
        return s1.substring(flag, flag + max);
    }