pku 1018

写了两三个版本，最后这个效率最高

#include <cstdio>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <set>
#define out(v) cout << #v << ": " << (v) << endl
#define MP(X,Y) make_pair(X,Y)
using namespace std;
typedef long long LL;
typedef pair<int, int> pr;
int T, n;
vector<pr> dev[105], allw;
int idx[105];

int main() {
	scanf("%d", &T);
	while (T--) {
		scanf("%d", &n);
		allw.clear();
		for (int i = 0; i < n; ++i) {
			int mi;
			scanf("%d", &mi);
			dev[i].resize(mi);
			for (int j = 0; j < mi; ++j) {
				scanf("%d%d", &dev[i][j].first, &dev[i][j].second);
				allw.push_back(MP(dev[i][j].first, i));
			}
			sort(dev[i].begin(), dev[i].end());	
			for (int j = mi - 2; j >= 0; --j)
				dev[i][j].second = min(dev[i][j].second, dev[i][j + 1].second);
			idx[i] = 0;
		}
		sort(allw.begin(), allw.end());
		int cost = 0;
		for (int j = 0; j < n; ++j) cost += dev[j][0].second;
		double ans = (double)allw[0].first / cost;
		
		for (int i = 1; i < allw.size(); ++i) {
			int row = allw[i - 1].second;
			cost -= dev[row][idx[row]].second;
			if (idx[row] + 1 == dev[row].size()) break;
			cost += dev[row][++idx[row]].second;
			ans = max(ans, (double)allw[i].first / cost);
		}
		printf("%.3f\n", ans);
	}
	return 0;
}