10012 - How Big Is It?

/****************************************** *(圆排列问题) 用center计算圆心因为圆与前面的圆相切，但不一定是它的前一个 */#include <cstdio>#include <algorithm>#include <cmath>#include <climits>using namespace std;const int N = 10;double r[N], x[N];int m;double ans = INT_MAX;void BackTrace(int t);double center(int t);void compute();int main(){int n;#ifndef ONLINE_JUDGEfreopen("d:\\OJ\\uva_in.txt", "r", stdin);#endifscanf("%d", &n);while (n--) {scanf("%d", &m);ans = INT_MAX;for (int i = 0; i < m; i++)scanf("%lf", &r[i]);BackTrace(0);printf("%.3lf\n", ans);}return 0;}void BackTrace(int t){if (t >= m) compute();else {for (int i = t; i < m; i++) {swap(r[t], r[i]);double centerx = center(t);if (centerx + r[0] + r[t] < ans) {x[t] = centerx;BackTrace(t + 1);}swap(r[t], r[i]);}}}double center(int t){double temp = 0;for (int i = 0; i < t; i++) {double value = x[i] + 2 * sqrt(r[t] * r[i]);if (value > temp) temp = value;}return temp;}void compute(){double high = 0, low = 0;for (int i = 0; i < m; i++) {if (x[i] - r[i] < low) low = x[i] - r[i];if (x[i] + r[i] > high) high = x[i] + r[i];}if (high - low < ans) ans = high - low;}