本文主要是介绍HDU 1325(并查集判断一个图是否是一棵树)，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
题意：每组数据都以0 0结束，-1 -1结束程序。 每组数据中的每两个数字为一小组，前一个数字代表的结点指向后一个数字代表的结点。
#include <iostream>
#include <cstring>
using namespace std;
int father[100010];
int find_father(int x)
{
while (father[x] != x)
x = father[x];
return x;
}
bool is_father(int s, int f)
{
while (father[s] != f)
{
if (father[s] == s) return false;
s = father[s];
}
return true;
}
int main()
{
int cases = 0;
int max_node, root, f, s;
bool ok;
while (cin >> f >> s, f >= 0 && s >= 0)
{
ok = true;
memset(father, 0, sizeof(father));
root = -1;
max_node = 0;
while (f || s)
{
if (max_node < f) max_node = f;
if (max_node < s) max_node = s;
if (father[f] == 0) father[f] = f;
if (father[s] == 0) father[s] = s;
if (father[s] != s) ok = false;
else if (!is_father(f, s)) father[s] = f;
else ok = false;
cin >> f >> s;
}
cases++;
cout << "Case " << cases << " is ";
if (ok)
for (int i = 1; i <= max_node; ++i)
{
if (father[i] == 0) continue;
int t = find_father(i);
if (t != root)
{
if (root == -1)
root = t;
else
{
ok = false;
break;
}
}
}
if (!ok) cout << "not a tree." << endl;
else cout << "a tree." <<endl;
}
}
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