Map

1 使用

1 声明

/*声明map*/map<int, string> myMap = {{1, "Apple"}, {2, "Banana"}, {3, "Orange"}};

2 插入元素

myMap.insert(make_pair(4, "Graphes"));

3 通过访问键查找和访问元素

cout << myMap[2] << endl;

4 遍历并打印map中元素

for(const auto& pair : myMap) {cout << "Key is: " << pair.first << ", Value is: " << pair.second << endl;
}

5 删除元素

myMap.erase(3);

6 判断指向某个键指向的键值对是否存在

if(myMap.count(3) == 0) {cout << "Key 3 not found" << endl;
}

7 清空map

myMap.clear()

8 完整代码

#include <bits/stdc++.h>
using namespace std;
int main() {/*声明map*/map<int, string> myMap = {{1, "Apple"}, {2, "Banana"}, {3, "Orange"}};/*插入元素*/myMap.insert(make_pair(4, "Grapes"));/*通过访问键查找和访问元素*/cout << myMap[2] << endl;/*遍历并打印map中元素*/for(const auto& pair : myMap) { //const auto& pair:用于遍历map的迭代器cout << "Key is " << pair.first << ", Value: " << pair.second << endl;}/*删除元素*/myMap.erase(3);     //这个是将整个key = 3的键值对删除了cout << "After delete key 3, the new map is:" << endl;for(const auto& pair : myMap) {cout << "Key is: " << pair.first << ", Value is: " << pair.second << endl;}/*判断指向某个键指向的键值对是否存在*/if(myMap.count(3) == 0) {cout << "Key 3 not found" << endl;}/*清空map*/myMap.clear();if(myMap.empty()) {cout << "Map is empty" << endl;}system("pause");return 0;
}

2 运用

2.1 主要思路：

1 使用map，其中每读取一个元素作为键，同时将这个键对应的值递增1
2 计算最少删除的元素数量时，如果当前键大于值，那么就将这个键清零；如果值大于键，那么就删除多余的

2.2 代码：

#include <bits/stdc++.h>
using namespace std;
int main() {map<int, int> myMap;int n;scanf("%d", &n);int data;for(int i = 0; i < n; i++) {scanf("%d", &data);myMap[data]++;}int count = 0;for(const auto& pair : myMap) {cout << pair.first << ' ' << pair.second << endl;if(pair.first < pair.second) {count += (pair.second - pair.second);}else if(pair.first > pair.second) {count += pair.second;}}cout << count << endl;return 0;
}