[LeetCode] 791. Custom Sort String

最新推荐文章于 2025-05-29 01:15:00 发布

carbon06

最新推荐文章于 2025-05-29 01:15:00 发布

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分类专栏： c++ leetcode 文章标签： leetcode sort 比较器

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本文介绍了一种基于定制排序的字符串处理算法，通过实现一个比较器并利用C++标准库中的sort函数，对输入字符串T进行排序，使得T中字符的顺序符合另一已排序字符串S的顺序。对于未出现在S中的字符，则可在T中保持任意位置。

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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.

思路

C++ 标准库中的sort 可以传入一个自己定制的比较函数或者比较器类。
所以可以实现一个比较器，由于S中只包含小写字母，所以可以使用一个长度为26的数组来记录字符出现的index，然后按照字符在数组中出现的先后顺序排序，具体实现如下：

class Solution {
public:
    struct CustomCmp
    {
        CustomCmp(const string& s)
        {
            chars_idx.resize(26,-1);

            for (int i = 0; i < s.size(); i++)
            {
                chars_idx[s[i]-'a'] = i;
            }
        }

        bool operator()(char c1, char c2) const
        {
            return (chars_idx[c1-'a'] < chars_idx[c2-'a']);
        }

        vector<int> chars_idx;
    };

    string customSortString(string S, string T) {
        CustomCmp cmp(S);
        sort(T.begin(),T.end(),cmp);
        return T;
    }
};