[leetcode] 791. Custom Sort String

[leetcode] 791. Custom Sort string

Description

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.

Note:

S has length at most 26, and no character is repeated in S.T has length at most 200.S and T consist of lowercase letters only.

分析

题目的意思是：字符串T按照字符串S的单词顺序排序。

原来就用一个hashmap先统计T的词频，然后按照S的顺序输出，最后把hashmap剩下的字符*词频加到res的尾部。string( size_type length, char ch ); 以length为长度的ch的拷贝（即length个ch）

代码

class Solution {public: string customSortString(string S, string T) { string res=""; unordered_map m; for(auto a:T){ m[a]++; } for(char a:S){ res+=string(m[a],a); m[a]=0; } for(auto a:m){ res+=string(a.second,a.first); } return res; }};

参考文献

​​[LeetCode] Custom Sort String 自定义排序的字符串​​​​标准C++中的string类的用法总结（转）​​

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