洛谷 P2920 [USACO08NOV]时间管理Time Management

时间管理Time Management

二分枚举开始时间。

#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
//Mystery_Sky
//
#define ll long long
#define M 10001000
#define INF 0x7f7f7f7f
ll l, r, mid;
int n;
struct node{
	int t, s;
}t[M];

inline bool cmp(node a, node b)
{
	return a.s < b.s;
}

inline bool check(ll ans)
{
	ll time = ans, cnt = 0;
	for(int i = 1; i <= n; i++) {
		ans += t[i].t;
		if(ans <= t[i].s) cnt++;
		else break;
	}
	return cnt == n;
}

int main() {
	scanf("%d", &n);
	for(int i = 1; i <= n; i++) scanf("%d%d", &t[i].t, &t[i].s);
	sort(t+1, t+1+n, cmp);
	l = 0, r = t[n].s;
	if(!check(0)) {
		printf("-1\n");
		return 0;
	}
	while(l < r) {
		mid = (l + r + 1)/2;
		if(check(mid)) l = mid;
		else r = mid - 1;
	}
	printf("%lld\n", l);
	return 0;
}