UVA 10012 How Big Is It?

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一定要注意边界的问题，第二个及以后的圆不一定是与它相邻的圆相切的，右边界也是。

#include<cstdio>#include<cstring>#include<iostream>#include<string>#include<algorithm>#include<math.h>using namespace std;const int maxn = 10;int t, n;int b[maxn], c[maxn];double a[maxn], w;double check(){double x[maxn] = { 0 }, m = 0;for (int i = 0; i < n; i++){x[i] = a[c[i]];for (int j = i - 1; j >= 0; j--)x[i] = max(x[i], x[j] + 2 * sqrt(a[c[i]] * a[c[j]]));}for (int i = 0; i < n; i++) m = max(m, x[i] + a[c[i]]);return m;}void work(int x){if (x == n){double k = check();w = min(k, w);return;}for (int i = 1; i <= n;i++)if (b[i]){b[i] = 0;c[x] = i;work(x + 1);b[i] = 1;}}int main(){cin >> t;while (t--){cin >> n;w = 1000000000;for (int i = 1; i <= n; i++) cin >> a[i], b[i] = 1;work(0);printf("%.3lf\n", w);}return 0;}