Ultraviolet A 11853-paintball (DFS)

Ultraviolet A 11853-paintball

Question Link

It is to give some circles and determine whether they can go from the left to the right without passing through these circles. If you can ask the start and end positions to the north as far as possible, the output position

Idea: Every time I find a circle DFS that exceeds the upper boundary, if it can reach the lower boundary, it will be unable to reach the partition. If it is left and right boundary, I need to update the answer value.

Code:

#include <cstdio>#include <cstring>#include <cmath>#include <cstdlib>#include <algorithm>using namespace std;const int N = 1005;int n, vis[N];struct Circle {int x, y, r;void read() {scanf("%d%d%d", &x, &y, &r);}} c[N];double ans1, ans2;bool can(Circle a, Circle b) {int dx = a.x - b.x;int dy = a.y - b.y;return dx * dx + dy * dy - (a.r + b.r) * (a.r + b.r) <= 0;}bool dfs(int u) {vis[u] = 1;if (c[u].y - c[u].r <= 0) return false;if (c[u].x - c[u].r <= 0) ans1 = min(ans1, c[u].y - sqrt(c[u].r * c[u].r - c[u].x * c[u].x));if (1000 - c[u].x - c[u].r <= 0) ans2 = min(ans2, c[u].y - sqrt(c[u].r * c[u].r - (1000 - c[u].x) * (1000 - c[u].x)));for (int i = 0; i < n; i++) {if (vis[i]) continue;if (can(c[u], c[i]))if (!dfs(i)) return false;}return true;}void solve() {ans1 = ans2 = 1000;for (int i = 0; i < n; i++) {if (!vis[i] && c[i].y + c[i].r >= 1000)if (!dfs(i)) {printf("IMPOSSIBLE\n");return;}}printf("0.00 %.2lf 1000.00 %.2lf\n", ans1, ans2);}int main() {while (~scanf("%d", &n)) {for (int i = 0; i < n; i++) {c[i].read();vis[i] = 0;}solve();}return 0;}

Ultraviolet A 11853-paintball (DFS)