bzoj1651: [Usaco2006 Feb]Stall Reservations 专用牛棚

Oh those picky N (1 <= N <= 50,000) cows! They are so picky that each one will only be milked over some precise time interval A..B (1 <= A <= B <= 1,000,000), which includes both times A and B. Obviously, FJ must create a reservation system to determine which stall each cow can be assigned for her milking time. Of course, no cow will share such a private moment with other cows. Help FJ by determining: * The minimum number of stalls required in the barn so that each cow can have her private milking period * An assignment of cows to these stalls over time

有N头牛,每头牛有个喝水时间,这段时间它将专用一个Stall 现在给出每头牛的喝水时间段,问至少要多少个Stall才能满足它们的要求

* Line 1: A single integer, N

* Lines 2..N+1: Line i+1 describes cow i‘s milking interval with two space-separated integers.

* Line 1: The minimum number of stalls the barn must have.

* Lines 2..N+1: Line i+1 describes the stall to which cow i will be assigned for her milking period.

不妨试下这个数据,对于按结束点SORT,再GREEDY的做法 1 3 5 7 6 9 10 11 8 12 4 13 正确的输出应该是3

/*
红果果的差分题目 
*/
#include<iostream>
#include<cstdio>
#include<cstring>

#define N 500001

using namespace std;
int a[N<<2],l,r,n,m,L,R,ans;

int main()
{
    scanf("%d",&n);L=1,R=1000000;
    for(int i=1;i<=n;i++)
    {
        scanf("%d%d",&l,&r);
        a[l]++;a[r+1]--;
    }
    int tot=0;
    for(int i=L;i<=R;i++)
    {
        tot+=a[i];
        ans=max(ans,tot);
    }
    printf("%d\n",ans);
    return 0;
}