2016 Multi-University Training Contest 2 1009 It's All In The Mind

題目鏈接：點擊打開鏈接

題目大意：給你一個n位的不上升數組，這個數組現在只有m位數字是可以確定的，問前兩位除以總和的最小值。

解題思路：貪心，讓前兩位儘可能的大，後面儘可能的小，注意不上升的約束條件就好了，本質上還是一道水題。

代碼：

#include<iostream>
#include<vector>
#include<cmath>
#include<algorithm>
#include<ctime>
#include "cstdio"
#include "string"
#include "string.h"
#include "map"
using namespace std;
int gcd(int a, int b)
{
	return (b>0) ? gcd(b, a%b) : a;
}

int a[101];
int main()
{
	int T,m,n;
	scanf("%d", &T);
	while (T--)
	{
		memset(a, -1, sizeof(a));
		scanf("%d %d", &n, &m);
		for (int i = 0;i < m;i++)
		{
			int x, y;
			scanf("%d %d", &x, &y);
			a[x] = y;
		}
		if (a[1] == -1)
			a[1] = 100;
		if (a[2] == -1)
			a[2] = min(100,a[1]);
		int sum = a[1] + a[2];
		int now = 0;
		for (int i = n;i >= 3;i--)
		{
			if (a[i] == -1)
				a[i] = now;
			else
				now = a[i];
			sum += a[i];
		}
		int fenzi = a[1] + a[2];
		if (fenzi == 0)
		{
			puts("0/1");
			continue;
		}
		int temp = gcd(fenzi, sum);
		printf("%d/%d\n", fenzi / temp, sum / temp);
	}
	return 0;
}

a1+a2∑ni=1aia1+a2∑ni=1aia1+a2∑ni=1aia1+a2∑ni=1ai