如何用C++制作LeetCode刷题小技巧-错题记录本

#include<bits/stdc++.h>
 using namespace std;
tyedef pair<string, int> Pair;
 //第3参数为函数名
bool my_compare(const Pair &p1, const Pair &p2){
	return p1.second < p2.second;
}
 //第3参数为重载了operator()操作符的类对象
struct MyCompare{
public:
	bool operator()(const Pair &p1, const Pair &p2) const{
		return p1.second < p2.second;
	}
};
int main(){
	map<string, int> test;
	test["Alice"] = 3;
	test["Cindy"] = 5;
	test["Bob"] = 7;
 	cout << "> sort by key" << endl;
	for(auto itr = test.begin(); itr != test.end(); ++itr){
		cout << itr->first << ": " << itr->second << endl;
	}
	cout << endl;
 	vector<Pair> vec;
 	for(auto itr = test.begin(); itr != test.end(); ++itr){
		vec.push_back(make_pair(itr->first, itr->second));
	}
 	sort(vec.begin(), vec.end(), MyCompare()); //my_compare或者MyCompare()都可以
 	cout << "> sort by value" << endl;
	for(auto itr = vec.begin(); itr != vec.end(); ++itr){
		cout << itr->first << ": " << itr->second << endl;
	}
 	return 0;
}

#include<bits/stdc++.h>
 using namespace std;
typedef pair<string, int> Pair;
 int main(){
	map<string, int> test;
	test["Alice"] = 3;
	test["Cindy"] = 5;
	test["Bob"] = 7;
 	cout << "> sort by key" << endl;
	for(auto itr = test.begin(); itr != test.end(); ++itr){
		cout << itr->first << ": " << itr->second << endl;
	}
	cout << endl;
 	map<int, string> result;
	transform(test.begin(), test.end(), inserter(result, result.begin()), [](pair<string, int> a) { return pair<int, string>(a.second, a.first); });
 	cout << "> sort by value" << endl;
	for(auto itr = result.begin(); itr != result.end(); ++itr){
		cout << itr->first << ": " << itr->second << endl;
	}
 	return 0;
}

 template pair make_pair(T1 a, T2 b) { return pair(a, b); }

bool isPrime( int num )
{
    //两个较小数另外处理
    if(num == 2||num == 3 )
        return 1;
    //不在6的倍数两侧的一定不是质数
    if(num % 6 != 1&&num % 6 != 5)
        return 0;
    int tmp = sqrt(num);
    //在6的倍数两侧的也可能不是质数
    for(int i = 5;i <= tmp;i += 6)
        if(num %i == 0||num % (i+ 2) == 0)
            return 0;
    //排除所有，剩余的是质数
    return 1;
 }

class Solution {
public:
	string removeOuterParentheses(string S) {
		string res = "";
        int a[S.length()+1];
        int flag=0;
        for(int i=0;i<S.length();i++)
        {
            if(S[i]=='(')
            {
                flag++;
                a[i]=flag;
            }
            else{
                flag--;
                a[i]=flag;
            }
        }
        for(int i=0;i<S.length();i++)
        {
            if(S[i]=='('&&a[i]==1)
            {
            }
            else if(S[i]==')'&&a[i]==0)
            {
 
            }
            else res.push_back(S[i]);
        }
		return res;
	}
};

 class Solution {
public:
	string removeOuterParentheses(string S) {
		string res = "";
		stack<char> a;
         for(auto b:S)
        {
            if(b=='(')
            {
                if(!a.empty())
                    res.push_back('(');// 表示非外部
                a.push('(');
             }
            else{
                if(a.size()!=1){// 表示非外部
                    res.push_back(')');
                }
                a.pop();
            }
        }
		return res;
	}
};

2，347. 前 K 个高频元素：

 typedef pair<int,int> Pair;
  
 bool my_compare(const Pair &p1, const Pair &p2){
        return p1.second > p2.second;
}
class Solution {
public:
     vector<int> topKFrequent(vector<int>& nums, int k) {
        map<int,int>mymap;
        vector<Pair> v;
        vector<int> res;
        for(auto i:nums)
        {
            mymap[i]+=1;
        }
        for(auto itr = mymap.begin(); itr != mymap.end(); ++itr)
		v.push_back(make_pair(itr->first, itr->second));
  
 		sort(v.begin(),v.end(),my_compare);
  		for(int i=0;i<k;i++)
        {
           res.push_back(v[i].first);
        }
        return res;
    }
};

class Solution {
public:
    static bool cmp(pair<int, int>& m, pair<int, int>& n) {
        return m.second > n.second;
    }
     vector<int> topKFrequent(vector<int>& nums, int k) {
        unordered_map<int, int> occurrences;
        for (auto& v : nums) {
            occurrences[v]++;
        }
         // pair 的第一个元素代表数组的值，第二个元素代表了该值出现的次数
        priority_queue<pair<int, int>, vector<pair<int, int>>, decltype(&cmp)> q(cmp);
        for (auto& [num, count] : occurrences) {
            if (q.size() == k) {
                if (q.top().second < count) {
                    q.pop();
                    q.emplace(num, count);
                }
            } else {
                q.emplace(num, count);
            }
        }
        vector<int> ret;
        while (!q.empty()) {
            ret.emplace_back(q.top().first);
            q.pop();
        }
        return ret;
    }
};

class Solution {
public:
    bool isUgly(int n) {
        if (n <= 0) return false;
        while (n % 2 == 0) n /= 2;
        while (n % 3 == 0) n /= 3;
        while (n % 5 == 0) n /= 5;
        return n == 1;
    }
};