JZOJ 5346. 【NOIP2017提高A组模拟9.5】NYG的背包

题目

分析

很神奇的贪心

(Code)

#include<cstdio>
#include<algorithm>
using namespace std;
typedef long long LL;

const int N = 100005;
int n , T , cnt1 , cnt2;
LL v;
struct node{
	int a , b;
}p[N] , q[N];

bool cmp1(node x , node y){return x.a < y.a;}
bool cmp2(node x , node y){return x.b < y.b;}

int main()
{
	freopen("backpack.in" , "r" , stdin);
	freopen("backpack.out" , "w" , stdout);
	scanf("%d" , &T);
	while (T--)
	{
		scanf("%d%lld" , &n , &v);
		cnt1 = cnt2 = 0;
		int fl = 1 , a , b;
		for(register int i = 1; i <= n; i++)
		{
			scanf("%d%d" , &a , &b);
			if (a <= b) p[++cnt1] = node{a , b};
			else q[++cnt2] = node{a , b};
		}
		sort(p + 1 , p + cnt1 + 1 , cmp1);
		for(register int i = 1; i <= cnt1; i++)
		{
			a = p[i].a , b = p[i].b;
			if (v < a){fl = 0; break;}
			v = v - a + b;
		}
		if (fl == 0){printf("No
"); continue;}
		sort(q + 1 , q + cnt2 + 1 , cmp2);
		for(register int i = 1; i <= cnt2; i++) v = v - q[i].a + q[i].b;
		for(register int i = 1; i <= cnt2; i++)
		{
			a = q[i].a , b = q[i].b;
			if (v < b){fl = 0; break;}
			v = v - b + a;
		}
		if (fl == 0){printf("No
"); continue;}
		printf("Yes
");
	}
}