[二分] 左右差值最小时答案尽可能大 UVALive 7261

二分面积差最小答案
暴力往右枚举判断面积差是否变化

#include<bits/stdc++.h>
#define ll long long
using namespace std;

const int mn = 10010;

struct node
{
	int l, r, w, h;
} s[mn];

int N;
ll check(int mid)
{
	ll sl = 0, sr = 0;
	for (int i = 1; i <= N; i++)
	{
		if (s[i].r <= mid)
			sl += (ll)s[i].w * s[i].h;
		else if (s[i].l >= mid)
			sr += (ll)s[i].w * s[i].h;
		else
		{
			sl += (ll)s[i].h * (mid - s[i].l);
			sr += (ll)s[i].h * (s[i].r - mid);
		}
	}
	return sl - sr;
}
int main()
{
	int T;
	scanf("%d", &T);
	while (T--)
	{
		int R;
		scanf("%d", &R);
		scanf("%d", &N);
		for (int i = 1; i <= N; i++)
		{
			int l, t, w, h;
			scanf("%d %d %d %d", &l, &t, &w, &h);
			s[i].l = l, s[i].r = l + w, s[i].w = w, s[i].h = h;
		}
		
		int ans = -1;
		int l = 0, r = R;
		ll area = 1e18;
		while (l <= r)
		{
			int mid = (l + r) / 2;
			ll t = check(mid);
			
			if (t < 0)
				l = mid + 1;
			else if (t >= 0) // 面积差尽可能小
			{
				area = min(area, t);
				r = mid - 1;
				ans = mid;
			}
		}
		
		while (ans < R && check(ans + 1) == area) // 面积差相同时 ans尽可能大
			ans++;
			
		printf("%d\n", ans);
	}
    return 0;
}