map<int, int> mp;
默认值为0- 访问某键值后,自动插入该pair
- 当值减少到0时,pair还存在于map中
针对2,3要手动erase元素
#include <bits/stdc++.h>
using namespace std;
void Judge(map<int, int> & has)
{
if(has.find(1) == has.end())
{
cout << "1 is not in map!" << endl;
}else
{
cout << "1 is already exist" << endl;
}
}
int main()
{
map<int, int> has;
Judge(has);
//1 is not in map!
cout << "has[1] = " << has[1] << endl;
//has[1] = 0
Judge(has);
//1 is already exist
has.erase(1);
Judge(has);
//1 is not in map
has[1] = 1;
has[1]--;
cout << "has[1] = " << has[1] << endl;
//has[1] = 0;
Judge(has);
//1 is already exist
return 0;
}