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题目链接

活动 - AcWing本课程系统讲解常用算法与数据结构的应用方式与技巧。https://www.acwing.com/problem/content/1252/

题解

当两个点已经是在同一个连通块中，再连一条边，就围成一个封闭的圈。一般用x * n + y的形式将（x, y）变成一维。

代码

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>using namespace std;const int N = 40010;int n, m;
int p[N];int get(int x, int y)
{return x * n + y;
}int find(int x)
{if (p[x] != x) p[x] = find(p[x]);return p[x];
}int main()
{cin >> n >> m;for (int i = 0; i < n * n; i++) p[i] = i;int res = 0;for (int i = 1; i <= m; i++){int x, y;char d;cin >> x >> y >> d;x--, y--;int a = get(x, y);int b;if (d == 'D') b = get(x + 1, y);else b = get(x, y + 1);int pa = find(a), pb = find(b);if (pa == pb){res = i;break;}p[pa] = pb;}if (!res) puts("draw");else cout << res << endl;return 0;
}

参考资料

1. AcWing算法提高课