Untitled

class Solution {
public:
    string shortestCommonSupersequence(string a, string b) {
        int n, m;
        n = a.length(); m = b.length();

        vector<vector<string>> dp(n+1, vector<string>(m+1, ""));
        for (int i=0; i<m; ++i) dp[n][i] = b.substr(i);
        for (int j=0; j<n; ++j) dp[j][m] = a.substr(j);

        for (int i=n-1; i>=0; --i){
            for (int j=m-1; j>=0; --j){
                if (a[i] == b[j]){
                    dp[i][j] = a[i] + dp[i+1][j+1];
                }
                else{
                    int l1 = dp[i+1][j].length();
                    int l2 = dp[i][j+1].length();

                    if (l1 < l2)
                        dp[i][j] = a[i] + dp[i+1][j];
                    else
                        dp[i][j] = b[j] + dp[i][j+1];
                }
            }
        }

        return dp[0][0];
    }
};