poj1308&&openjudge310:Is It A Tree?

這個題用並查集判斷有沒有森林就行了，注意一些細節的特特判，代碼寫的並不優美，剛開始思路有點亂，導致寫了很多囉嗦的東西，然後就懶得精簡了，-_-|||

#include <cstdio>
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
int fa[500000];
int in[500000];
bool flag = 0;
bool vis[5000000];
int find(int x)
{
    return fa[x] == x ? x : fa[x] = find(fa[x]);
}
int main()
{
    int x,y;int tot = 1;
    while(cin >>x>>y)
    {   
        int a,b;
        if(x == -1 && y == -1)
        break;
        else
        {
            memset(in,0,sizeof(in));
            memset(vis,0,sizeof(vis));
            memset(fa,0,sizeof(fa));
            if(x == 0 && y == 0)
            {
                printf("Case %d is a tree.\n",tot++);
                continue;
            }
            fa[y] = x;
            in[y] ++;
            vis[y] = 1;
            vis[x] = 1;
            while(cin>>a>>b)
            {           
                flag = 0;
                int x;
                int ans = 0;
                if(a == 0 && b == 0)
                {
                    for(int i = 1; i < 10000; i ++)
                    {
                        if(in[i] > 1)
                        {
                            flag = 1;
                        }
                        if(in[i] == 0 && vis[i])
                        {
                            x = i;
                            ans ++;
                        }
                    }
                    if(ans > 1 || ans == 0)
                    flag = 1;
                    else
                    for(int i = 1; i < 1000 ; i ++)
                    {
                        if(find(i) != find(x) && vis[i])
                        {
                            flag = 1;
                        }
                    }
                    if(flag)
                    printf("Case %d is not a tree.\n",tot++);
                    else
                    printf("Case %d is a tree.\n",tot++);
                    memset(in,0,sizeof(in));
                    memset(vis,0,sizeof(vis));
                    memset(fa,0,sizeof(fa));
                    break;
                }
                fa[b] = a;
                in[b]++;
                vis[b] = 1;
                vis[a] = 1;
                if(a == b)
                flag = 1;   
            }
        }
    }
    return 0;
}