leetcode 791. Custom Sort String

S and T are strings composed of lowercase letters. In S, no letter occurs more than once.

S was sorted in some custom order previously. We want to permute the characters of T so that they match the order that S was sorted. More specifically, if x occurs before y in S, then x should occur before y in the returned string.

Return any permutation of T (as a string) that satisfies this property.

Example :
Input: 
S = "cba"
T = "abcd"
Output: "cbad"
Explanation: 
"a", "b", "c" appear in S, so the order of "a", "b", "c" should be "c", "b", and "a". 
Since "d" does not appear in S, it can be at any position in T. "dcba", "cdba", "cbda" are also valid outputs.

这道题目很easy啊，只要明白题意，直接2重循环去找就行了。

class Solution {
public:
    string customSortString(string S, string T) {
        int n = T.size();
        vector<int> vis(n);
        string ans = "";
        for (int i = 0; i < S.size(); ++i) {
            for (int j = 0; j < n; ++j) {
                if (!vis[j] && S[i] == T[j]) {
                    ans += T[j];
                    vis[j] = 1;
                }
            }
        }
        for (int i = 0; i < T.size(); ++i) {
            if (!vis[i]) ans += T[i];
        }
        return ans;
    }
};