alg-最长公共子序列

class Solution {
public:
    std::string LongestCommonSubsequence(const std::string& s1, const std::string& s2) {
        if (s1.empty()||s2.empty()) {
            return 0;
        }

        //dp
        std::vector<std::vector<int>> dp(s1.size()+1,std::vector<int>(s2.size()+1,0));
        for(int i=1;i<s1.size()+1;i++) {
            for(int j=1;j<s2.size()+1;j++) {
                dp[i][j]=(s1[i-1]==s2[j-1])?dp[i-1][j-1]+1:std::max(dp[i-1][j],dp[i][j-1]);
            }
        }

        //search path
        std::string res;
        for(int i=s1.size(),j=s2.size();i>0&&j>0;) {
            if(s1[i-1]==s2[j-1]) {
                res.insert(0,1,s1[i-1]);
                i--;
                j--;
            }
            else {
                if(dp[i-1][j]>dp[i][j-1]) {
                    i--;
                }
                else {
                    j--;
                }
            }
        }
        
        return res;
    }  
};