POJ(2431)Expedition

利用优先队列，找出经过加油站的最大油量，重复操作。

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <queue>
using namespace std;
const int maxn = 10005;
struct stop{
    int d,f;
    friend bool operator<(const stop &a,const stop &b){
        return a.d<b.d;
    }
}st[maxn];

int main(){
    int n;
    while(~scanf("%d",&n)){
        priority_queue<int>que;
        for(int i = 0;i < n;i++)
            scanf("%d%d",&st[i].d,&st[i].f);
        int L,P;
        scanf("%d%d",&L,&P);
        for(int i = 0;i < n;i++)
            st[i].d = L - st[i].d;
        int ans = 0;
        int pos = 0;
        st[n].d = L;
        st[n].f = 0;
        sort(st, st+n+1);
        int flag = 1;
        for(int i = 0;i <= n;i++){
            int temp = st[i].d - pos;
            while(P < temp){
                if(que.empty()){
                    flag = 0;
                    break;
                }
                P += que.top();
                que.pop();
                ans++;
            }
            P -= temp;
            pos = st[i].d;
            que.push(st[i].f);
        }
        if(flag)
            printf("%d\n",ans);
        else
            printf("-1\n");
    }
    return 0;
}