跟着chengyulala刷题之[kuangbin带你飞]之'并查集'专题/斜眼笑

 1 #include<cstdio>
 2 #include<cstring>
 3 using namespace std;
 4 
 5 const int MAXN = 1e3+5;
 6 
 7 inline int read() {
 8     char c = getchar(); int s = 0, f = 1;
 9     while(c < ‘0‘ || c > ‘9‘) { if(c == ‘-‘) f = -1; c = getchar(); }
10     while(c >= ‘0‘ && c <= ‘9‘)  s = s*10 + c-‘0‘, c = getchar();
11     return s*f;
12 }
13 
14 int p[MAXN];
15 
16 inline int find(int x) { return p[x] == x ? x : p[x] = find(p[x]); }
17 
18 int main() {
19     int s, e;
20     int T = 1;
21     while(1) {
22         bool flag = true;
23         while(1) { //scanf("%d%d", &s, &e) == 2 && s
24             s = read(), e = read();
25             if(s == 0 && e == 0) break;
26             if(s == -1) return 0;
27             if(!p[s]) p[s] = s;
28             if(!p[e]) p[e] = e;
29             int x = find(s);
30             int y = find(e);
31             if(x == y) flag = false;
32             else p[x] = y;
33         }
34         int ans = 0;
35         for(int i = 1; i <= MAXN; ++i) {
36             if(p[i] == i) ans++;
37             p[i] = 0;
38         }
39 
40         printf("Case %d is ", T++);
41         if(!flag || ans > 1) printf("not a tree.\n");
42         else printf("a tree.\n");
43     }
44     return 0;
45 }