GCJ2017R1C A. Ample Syrup

题目大意

给$n$个圆盘，取$k$个组成一个stack，要求表面积最大

简要题解

按侧面积排序取最大的前$k-1$个，再枚举剩下的一个加入求总面积取最大值即可。

#include <vector>
#include <algorithm>
#include <iostream>
using namespace std;

using DB = double;
using II = pair<int, int>;
using VII = vector<pair<int, int> >;
const DB PI = 3.1415926535897932384;


DB getSide(II p) {
    return 2.0 * PI * p.first * p.second;
}

bool cmp(II a, II b) {
    return getSide(a) > getSide(b);
}

int main() {
    freopen("A.in", "r", stdin);
    freopen("A.out", "w", stdout);
    int T; cin >> T;
    for (int kase = 1; kase <= T; ++kase) {
        int n, k; cin >> n >> k;
        vector<pair<int, int> > p(n);
        for (int i = 0; i < n; ++i)
            cin >> p[i].first >> p[i].second;
        sort(p.begin(), p.end(), cmp);
        DB ans = 0;
        DB tmp = 0;
        int maxR = 0;
        for (int i = 0; i < k - 1; ++i) {
            tmp += getSide(p[i]);
            maxR = max(maxR, p[i].first);
        }
        for (int i = k - 1; i < n; ++i) {
            ans = max(ans, tmp + getSide(p[i]) + 
                    PI * max(maxR, p[i].first) * max(maxR, p[i].first));
        }

        printf("Case #%d: %.12lf
", kase, ans);
    }

    return 0;
}