例题7-7(uva-1354)

#include <iostream>
#include <istream>
#include <sstream>
#include <vector>
#include <stack>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
#include <algorithm>
#include <numeric>
#include <chrono>
#include <ctime>
#include <cmath>
#include <cctype>
#include <string>
#include <cstdio>
#include <iomanip>


#include <thread>
#include <mutex>
#include <condition_variable>
#include <functional>
#include <iterator>
using namespace std;
const int maxn = 10;
int n, cnt,vis[maxn];
double width,w[maxn],l[maxn],r[maxn],res;

void dfs(int cur) {
	if (cur >= cnt) {
		for (int i = 0; i < cnt; i++) {
			if(vis[i]) continue;
			if(l[i] + r[i] > width) continue;
			res = max(l[i] + r[i], res);
		}
		return;
	}

	//任选2个 合并为一个
	for (int i = 0;i< cnt;i++)
	{
		if (vis[i])continue;
		for (int j = 0; j < cnt; j++) {
			if(i == j || vis[j]) continue;
			//当前2个 挂件是如果挂的 i在左 j在右  
			//w[i] * left = w[j] * right
			//w[i] * left = w[j] * (1 - left)
			//w[i] * left + w[j] * left = w[j]
			//left = w[j] / (w[i] + w[j])
			double  left = w[j] / (w[i] + w[j]), right = 1 - left;
			w[j] += w[i];
			vis[i] = 1;
			double templ = l[j], tempr = r[j];
			//左右分别多宽 
			l[j] = max(l[i] + left, l[j] - right);
			r[j] = max(r[j] + right, r[i] - left);
			dfs(cur + 1);
			vis[i] = 0;
			w[j] -= w[i];
			l[j] = templ;
			r[j] = tempr;
		}
	}
}

int main()
{
	cin >> n;
	while (n--) {
		cin >> width >> cnt;
		res = -1;
		memset(vis, 0, sizeof(vis));
		memset(l, 0, sizeof(l));
		memset(r, 0, sizeof(r));

		for (int i = 0; i < cnt; i++) {
			cin >> w[i];
		}
		dfs(1);
		cout << fixed << setprecision(10) << res << endl;
	}
	return 0;
}