一些易忘的细节

1、priority_queue自定义比较结构

class Solution {
public:
    struct cmp
    {
        bool operator()(int &a, int &b) const
        {
        //因为优先出列判定为!cmp，所以反向定义实现最小值优先
            return a>b;
        }
    };
    vector<int> GetLeastNumbers_Solution(vector<int> input, int k) {
        if (input.size() == 0 || k == 0 || k > input.size()) return {};
        /*int start = 0, end = input.size()-1;
        int index = partition(input, start, end);
        while (index != k) {
            if (index > k-1) {
                end = 
            }
        }*/
        priority_queue<int, vector<int>, cmp> pq;
        for (int i = 0; i < input.size(); i++) {
                pq.push(input[i]);
        }
        vector<int> ans;
        for (int i = 0; i < k && !pq.empty(); i++) {
            ans.push_back(pq.top());
            pq.pop();
        }
        return ans;
    }
};

 leetcode767:

class Solution {
public:
    string reorganizeString(string S) {
        vector<int> cnt(26, 0);
        for (int i = 0; i < S.size(); i++) {
            cnt[S[i]-'a']++;
            if (cnt[S[i]-'a'] > (S.size()+1)/2) return "";
        }
        auto cmp = [&cnt](int i, int j) { 
            return cnt[i] < cnt[j]; 
        };
        priority_queue<int, vector<int>, decltype(cmp)> pq(cmp);
        for (int i = 0; i < 26; i++) 
            if (cnt[i] > 0) pq.push(i);
        for (int i = 0, prev = -1; i < S.size(); i++) {
            int j = pq.top();
            pq.pop();
            S[i] = 'a'+j;
            if (prev >= 0) pq.push(prev);
            prev = --cnt[j] <= 0 ? -1 : j;
        }
        return S;
    }
};