Codeforces Round #363 (Div. 1) B. Fix a Tree 树的拆环

题目链接：http://codeforces.com/problemset/problem/698/B
题意：告诉你n个节点当前的父节点，修改最少的点的父节点使之变成一棵有根树。
思路：拆环。
题解：http://codeforces.com/blog/entry/46148
代码：

#include <cstdio>
const int maxn = 200200;
int f[maxn], vis[maxn], n, s, cnt, idx;
int Find(int x)
{
vis[x] = ++ idx;
while (!vis[ f[x] ])
{
x = f[x];
vis[x] = idx;
}
if (vis[ f[x] ] == idx)
{
if (s == 0)
s = x;
if (f[x] != s)
{
f[x] = s;
cnt ++;
}
}
}
int main()
{
scanf("%d", &n);
for (int i = 1; i <= n; i ++)
scanf("%d" , f + i);
for (int i = 1; i <= n; i ++)
if (i == f[i])
s = i;
for (int i = 1; i <= n; i ++)
if (!vis[i])
Find(i);
printf("%d\n", cnt);
for (int i = 1; i <= n; i ++)
printf("%d ", f[i]);
return 0;
}