poj 3431 Expedition 优先队列

#include <iostream>
#include <algorithm>
#include <stdio.h>
#include <queue>
using namespace std;
const int maxn = 10005;
struct node {
    int a,b;
} ans[maxn];
bool cmp(const node& x, const node& y) {return x.a<y.a;}
priority_queue<int,vector<int>,less<int> > q;
int main() {
    int n,l,p;
    scanf("%d",&n);
    for(int i=0;i<n;++i) scanf("%d %d",&ans[i].a,&ans[i].b);
    scanf("%d %d",&l,&p);
    for(int i=0;i<n;++i) ans[i].a=l-ans[i].a;
    ans[n].a=l;
    ans[n].b=0;
    n++;
    sort(ans,ans+n,cmp);
    int index=0,last=p,cnt=0;
    for(int i=0;i<n;++i) {
        int dist=ans[i].a-index;
        while(dist>last) {
            if(q.empty()) {
                puts("-1\n");
                return 0;
            }
            last+=q.top();
            q.pop();
            cnt++;
        }
        last-=dist;
        index=ans[i].a;
        q.push(ans[i].b);
    }
    printf("%d\n",cnt);
    return 0;
}