Is It A Tree? POJ - 1308

版权声明： https://blog.csdn.net/weixin_40959045/article/details/88382019

判断边数是否是点数-1 还有特例

#include <cstdio>
#include <cstring>
using namespace std;
#define sci(num) scanf("%d",&num)
#define  mem(a,b) memset(a,b,sizeof a)
const int MAX_N = 1000005;
int F[MAX_N];
bool vis[MAX_N];
int Find(int x) {
    return F[x] == x ? x : F[x] = Find(F[x]);
}
void init() {
    for (int i = 0;i < MAX_N;i++) {
        vis[i] = false;
        F[i] = i;
    }
}
int main() {
    int cnt_cs = 1;
    int cnt_v = 0;
    int cnt_u = 0;
    int u,v;
    while (~scanf("%d%d",&u,&v)) {
        if (u == -1 && v == -1) break;
        init();
        cnt_u = cnt_v = 0;
        bool judge =  true;
        do {
            if (u == 0 || v == 0) break;
            if (!vis[u]) cnt_v++,vis[u] = true;
            if (!vis[v]) cnt_v++,vis[v] = true;
            int fu = Find(u);
            int fv = Find(v);
            if (fv != v) {
                judge = false;
            } else if (fu == fv) {
                judge = false;
            } else {
                F[v] = u;
                cnt_u++;
            }
        } while (~scanf("%d%d",&u,&v));
        if (cnt_u + 1 != cnt_v) {
            judge = false;
        }
        if (cnt_u == 0 && cnt_v == 0) {
            judge = true;
        }
        if (judge) {
            printf("Case %d is a tree.\n",cnt_cs++);
        } else {
            printf("Case %d is not a tree.\n",cnt_cs++);
        }
    }

    return 0;
}