经历了TLE->WA，这题我记住了
1）不要用set
2）建议按照开始时间升序排序，维护一个结束时间的最小堆

代法附下：
#include <iostream>
#include <queue>
#include <utility>
#include <algorithm>
#include <cstdio>
using namespace std;

typedef pair<int, int> P;
struct Itv{
    int s, g;
    int order;
    bool operator < (const Itv& b) const
    {
        if(this->s != b.s)
            return this->s < b.s;
        else
            return this->g < b.g;
    }
};

const int maxn = 50000 + 5;
int N;
priority_queue<P, vector<P>, greater<P> > pq;
Itv itvs[maxn];
int stall[maxn];

int tanxin()
{
    pq.push(make_pair(itvs[0].g, 1));
    stall[itvs[0].order] = 1;
    for(int i = 1; i<N; i++)
    {
        P p = pq.top();
        if(itvs[i].s > p.first)
        {
            stall[itvs[i].order] = p.second;
            pq.pop();
            pq.push(make_pair(itvs[i].g, p.second));
        }
        else
        {
            stall[itvs[i].order] = pq.size() + 1;
            pq.push(make_pair(itvs[i].g, pq.size() + 1));
        }
    }

    return pq.size();
}

int main()
{
    scanf("%d", &N);
    for(int i = 0; i<N; i++)
    {
        scanf("%d %d", &itvs[i].s, &itvs[i].g);
        itvs[i].order = i;
    }

    sort(itvs, itvs + N);
    int minnum = tanxin();
    printf("%d\n", minnum);
    for(int i = 0; i<N; i++)
        printf("%d\n", stall[i]);

    return 0;
}