POJ 2010 - Moo University - Financial Aid(优先队列)

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题目:

http://poj.org/problem?id=2010

题意:

总费用为f,给你c头牛的分数和学费,从中选出n头牛,使其中位数最大且费用不超过总费用.

思路:

结构体记录分数和学费,按照分数从小到大排列.

使用优先队列预处理.先预处理出每个位置前面和后面的n/2头牛的最小花费,然后枚举每个位置,得到最后的答案.

AC.

#include <iostream>#include <cstdio>#include <queue>#include <set>#include <algorithm>#include <cstring>using namespace std;const int maxn = 100005;struct Num {    int score, aid;    bool operator < (const Num & X) const {        return score < X.score;    }}num[maxn];struct node {    int score, aid;    bool operator < (const node & X) const {        return aid < X.aid;    }};priority_queue<node> que;int pay[maxn], pay2[maxn];int n, c, f;int main(){//freopen("in", "r", stdin);    while(~scanf("%d %d %d", &n, &c, &f)) {        int mid = n/2;        for(int i = 0; i < c; ++i) {            scanf("%d %d", &num[i].score, &num[i].aid);        }        sort(num, num + c);        int sum = 0;        node now, tmp;        while(que.size()) que.pop();        for(int i = 0; i < c-mid; ++i) {            now.score = num[i].score; now.aid = num[i].aid;            if(i >= mid) {                pay[i] = num[i].aid + sum;                sum += num[i].aid;                que.push(now);                tmp = que.top(); que.pop();                sum -= tmp.aid;            }            else {                que.push(now);                sum += num[i].aid;            }        }        sum = 0;        while(que.size()) que.pop();        for(int i = c-1; i >= mid; --i) {            now.score = num[i].score; now.aid = num[i].aid;            if(c - i > mid) {                pay2[i] = sum;                sum += num[i].aid;                que.push(now);                tmp = que.top(); que.pop();                sum -= tmp.aid;            }            else {                que.push(now);                sum += num[i].aid;            }        }        int ans = -1;        for(int i = mid; i + mid < c; ++i) {            if(pay[i] + pay2[i] <= f) ans = num[i].score;        }        printf("%d\n", ans);    }    return n;}

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