791. Custom Sort String

You are given two strings order and s. All the words of order are unique and were sorted in some custom order previously.

Permute the characters of s so that they match the order that order was sorted. More specifically, if a character x occurs before a character y in order, then x should occur before y in the permuted string.

Return any permutation of s that satisfies this property.

class Solution {
public:
    string customSortString(string order, string s) {
        int o = 1;
        unordered_map<char, int> mp;
        for(auto& ch : order)
            mp[ch] = o++;
        sort(begin(s), end(s), [&](char a, char b) {
            return mp[a] < mp[b];
        });
        return s;
    }
};