题解 | #最长公共子序列(二)#

import java.util.*;


public class Solution {
    /**
     * longest common subsequence
     * @param s1 string字符串 the string
     * @param s2 string字符串 the string
     * @return string字符串
     */
    public String LCS (String s1, String s2) {
        // write code here
        int m = s1.length();
        int n = s2.length();
        if(m == 0 || n == 0) {
            return "-1";
        }
        char[] arr1 = s1.toCharArray();
        char[] arr2 = s2.toCharArray();
        String[][] dp = new String[m + 1][n + 1];
        for(int i = 0; i < dp.length; i++) {
            dp[i][0] = "";
        }
        for(int i = 0; i < dp[0].length; i++) {
            dp[0][i] = "";
        }
        int maxVal = 0, lastI = -1, lastJ = -1;
        for(int i = 0; i < m; i++) {
            for(int j = 0; j < n; j++) {
                if(arr1[i] == arr2[j]) {
                    dp[i + 1][j + 1] = dp[i][j] + arr1[i];
                    if(dp[i + 1][j + 1].length() > maxVal) {
                        maxVal = dp[i + 1][j + 1].length();
                        lastI = i + 1;
                        lastJ = j + 1;
                    }
                } else {
                    if(dp[i][j + 1].length() > dp[i + 1][j].length()) {
                        dp[i + 1][j + 1] = dp[i][j + 1];
                    } else {
                        dp[i + 1][j + 1] = dp[i + 1][j];
                    }
                }
            }
        }
        if(maxVal == 0) {
            return "-1";
        }
        return dp[lastI][lastJ];
    }
}