题解 | #最长公共子序列(二)#

class Solution {
  public:
    string LCS(string s1, string s2) {
        int n = s1.length(), m = s2.length();

        if (s1.empty() || s2.empty()) return "-1";

        vector<vector<int>> dp(n + 1, vector<int>(m + 1));
        string res;

        for(int i = 1; i <= n; ++ i){
            for(int j = 1; j <= m; ++ j){
                dp[i][j] = (s1[i - 1] == s2[j - 1]) ? 1 + dp[i- 1][j - 1] : max(dp[i][j - 1], dp[i - 1][j]);
            }
        }

        for(int i = n, j = m; dp[i][j] > 0; ){
            if(s1[i - 1] == s2[j - 1]){
                res += s1[i - 1];
                i --;
                j --;
            }else if(dp[i - 1][j] >= dp[i][j - 1]){
                i --;
            }else{
                j --;
            }
        }

        reverse(res.begin(), res.end());
        return res != "" ? res : "-1";

    }
};