题解 | 大整数哈希

#include <iostream>
#include <unordered_map>
using namespace std;

int main() {

    unordered_map<unsigned long long, unsigned long long> f;//定义f
    unsigned long long n;
    cin >> n;
    unsigned long long res = 0;//存放结果
    for(unsigned long long i = 1; i <= n; i++){
        unsigned long long x, y;
        cin >> x >> y;
        if(f.count(x)){//已经存在x则获取当前值给ans,更新res并更新f(x)
            unsigned long long ans = f[x];
            res += i *ans;
            f[x] = y;
        }
        else{//不存在x,ans值为0，不用更新res直接添加f(x)
            f[x] = y;
        }
    }
    printf("%llu",res);
    return 0;
}
// 64 位输出请用 printf("%lld")