【luogu P1314 聪明的质监员】 题解

题目链接：https://www.luogu.org/problemnew/show/P1314
二分答案
但是计算区间贡献的时候 直接暴力会挂
前缀和加速

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define ll long long
using namespace std;
const int maxn = 2000000 + 10;
ll w[maxn], v[maxn], pren[maxn], prev[maxn], l[maxn], r[maxn], n, m, S;
ll maxw = -9999999999999, minw = 9999999999999, ans = 9999999999999, now;
bool check(int W)
{
	ll Y = 0;
	memset(pren, 0, sizeof(pren));
	memset(prev, 0, sizeof(prev));
	for(int i = 1; i <= n; i++)
	{
		if(w[i] > W) pren[i] = pren[i-1] + 1, prev[i] = prev[i-1] + v[i];
		else pren[i] = pren[i-1], prev[i] = prev[i-1];
	}
	for(int i = 1; i <= m; i++)
	Y += (pren[r[i]] - pren[l[i]-1])*(prev[r[i]] - prev[l[i]-1]);
	now = abs(Y-S);
	if(Y > S) return true;
	return false;
}
int main()
{
	scanf("%lld%lld%lld",&n,&m,&S);
	for(int i = 1; i <= n; i++)
	{
		scanf("%lld%lld",&w[i],&v[i]);
		maxw = max(w[i], maxw);
		minw = min(w[i], minw);
	}
	for(int i = 1; i <= m; i++)
	scanf("%lld%lld",&l[i],&r[i]);
	ll left = minw - 1, right = maxw + 2, mid;
	while(left <= right)
	{
		int mid = (left + right)>>1;
		if(check(mid)) left = mid + 1;
		else right = mid - 1;
		if(ans > now) ans = now;
	}
	printf("%lld",ans);
}