Uva - 11853 - Paintball

来源：互联网发布：centos apache公网ip 编辑：程序博客网时间：2024/04/29 01:03

先判断是否有解，从上到下dfs判断连通性，如果有从顶部到底部连通图，则无解。再判断最北的进出位置，从上边界开始遍历，沿途检查与边界相交的圆。这些圆的左边界的交点中最靠南边的一个就是所有的最北进入位置，和右边的最南交点就是所求的最北离开位置。

AC代码：

#include <iostream>#include <cstdio>#include <cstdlib>#include <cctype>#include <cstring>#include <string>#include <sstream>#include <vector>#include <set>#include <map>#include <algorithm>#include <stack>#include <queue>#include <bitset> #include <cassert> #include <cmath>using namespace std;const int maxn = 1005;const double W = 1000.0;int n, vis[maxn];double x[maxn], y[maxn], r[maxn], leftP, rightP;bool flag;// 判断c1和c2是否相交bool intersect(int c1, int c2){return sqrt((x[c1] - x[c2]) * (x[c1] - x[c2]) + (y[c1] - y[c2]) * (y[c1] - y[c2])) < r[c1] + r[c2];}void checkCircle(int u){if (x[u] - r[u] < 0) {leftP = min(leftP, y[u] - sqrt(r[u] * r[u] - x[u] * x[u]));}if (x[u] + r[u] > W) {rightP = min(rightP, y[u] - sqrt(r[u] * r[u] - (W - x[u]) * (W - x[u])));}}// 能不能到达底部bool dfs(int u){if (vis[u]) {return false;}vis[u] = 1;if (y[u] - r[u] < 0) {return true;}for (int v = 0; v < n; v++) {if (intersect(u, v) && dfs(v)) {return true;}}checkCircle(u);return false;}int main(){while (scanf("%d", &n) == 1) {flag = true;leftP = rightP = W; memset(vis, 0, sizeof(vis));for (int i = 0; i < n; i++) {scanf("%lf%lf%lf", &x[i], &y[i], &r[i]);}for (int i = 0; i < n; i++) {if (y[i] + r[i] >= W && dfs(i)) { // 从上面开始dfsflag = false;break;}}if (flag) {printf("0.00 %.2lf %.2lf %.2lf\n", leftP, W, rightP);}else {printf("IMPOSSIBLE\n");}}return 0;}

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