题解 | #最长公共子序列-II#

如果s1[i]==s2[j], dp[i][j] = dp[i-1][j-1] + 1

如果s1[i]!=s2[j], dp[i][j] = max(dp[i][j-1],dp[i-1][j])

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
        String[][] dp = new String[s1.length()+1][s2.length()+1];

        for (int i = 0; i <= s1.length(); i++) {
            dp[i][0] = "";
        }
        for (int i = 0; i <= s2.length(); i++) {
            dp[0][i] = "";
        }

        for (int i = 1; i <= s1.length(); i++) {
            for (int j = 1; j <= s2.length(); j++) {
                if (s1.charAt(i-1) == s2.charAt(j-1)) {
                    dp[i][j] = dp[i-1][j-1] + s1.charAt(i-1);
                } else {
                    if (dp[i][j-1].length() > dp[i-1][j].length()) {
                        dp[i][j] = dp[i][j-1];
                    } else {
                        dp[i][j] = dp[i-1][j];
                    }
                }
            }
        }
        if (dp[s1.length()][s2.length()].length() == 0) {
            return "-1";
        }
        return dp[s1.length()][s2.length()];
    }
}