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題意：

       判斷給出的線段是否組成了多邊形。

 

 

 

Solution：

             簡單題，並查集+hash

             這裡用map實現

 

code

#include <iostream>#include <cstdio>#include <utility>#include <map>using namespace std;typedef pair<int, int> ii;map<ii, int> f;int fa[400009];int n, xa, ya, xb, yb, cnt;int Find (int x) {if (fa[x] != x) return fa[x] = Find (fa[x]);return x;}int main() {scanf ("%d", &n);for (int i = 1; i <= 2 * n; i++) fa[i] = i;for (int i = 1; i <= n; i++) {scanf ("%d %d %d %d", &xa, &ya, &xb, &yb);ii tem1 = make_pair (xa, ya), tem2 = make_pair (xb, yb);if (f.count (tem1) == 0 ) f[tem1] = ++cnt;if (f.count (tem2) == 0 ) f[tem2] = ++cnt;int x = Find (f[tem1]), y = Find (f[tem2]);if (x != y)fa[x] = y;else {cout << i << endl;return 0;}}cout << 0 << endl;return 0;}