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
", cnt);
    for (int i = 1; i <= n; i ++)
        printf("%d ", f[i]);
    return 0;
}