1. 原題： https://www.patest.cn/contests/pat-a-PRactise/1048

2. 思路:

3. 源碼（已AC）：

#include<iostream>#include<map>using namespace std;int main(void){	//freopen("in.txt", "r", stdin);	int N, M;	cin >> N >> M;	map<int, int> monp;//key是面值，value是張數。	for (int i = 0; i < N; i++)//讀入數據	{		int val;		cin >> val;		if (monp.count(val) == 0)			monp[val] = 0;		monp[val]++;	}	map<int, int>::iterator it;	for (it = monp.begin(); it != monp.end() && it->first <= M/2; it++)//處理到小于等于M的一半就行	{		int sub_val = M - it->first;		if (sub_val == it->first && it->second > 1)//相同面值有多張		{			cout << sub_val << ' ' << sub_val << endl;			return 0;		}		if (sub_val != it->first && monp.count(sub_val) == 1)//不同面值		{			cout << it->first << ' ' << sub_val << endl;			return 0;		}	}	cout << "No Solution/n";	return 0;}