hdu 2818 Building Block(并查集)

每次总有新领悟。。

认为没堆最底层为祖先。

关于findset是怎么维护的，这次又好好理解了一下，这道题是每次更新x和x的上一层的结点，自底层向上(从祖先一层一层到本身)。

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstdlib>
 4 #include<cstring>
 5 #include<string>
 6 #include<queue>
 7 #include<algorithm>
 8 #include<map>
 9 #include<iomanip>
10 #include<climits>
11 #include<string.h>
12 #include<cmath>
13 #include<stdlib.h>
14 #include<vector>
15 #include<stack>
16 #include<set>
17 #define INF 1e7
18 #define MAXN 10010
19 #define maxn 1000010
20 #define Mod 1000007
21 #define N 1010
22 using namespace std;
23 typedef long long LL;
24
25 int n, m;
26 int fa[333333];
27 int num[333333];
28 int un[333333];
29
30 //取每一堆最底部的为祖先
31 //从祖先向下一层一层更新
32 int findset(int x)
33 {
34     if (x == fa[x]) return x;
35     int tmp = findset(fa[x]);
36     un[x] += un[fa[x]];
37     fa[x] = tmp;
38     return fa[x];
39 }
40
41 void merg(int a, int b)
42 {
43     int x = findset(a);
44     int y = findset(b);
45     if (x != y) {
46         un[x] = num[y];
47         num[y] += num[x];
48         fa[x] = y;
49     }
50 }
51
52 int main()
53 {
54     int a, b;
55     char ch;
56     while (~scanf("%d",&n)) {
57         getchar();
58         for (int i = 0; i <= n; ++i)
59             fa[i] = i, num[i] = 1,un[i] = 0;
60
61         for (int i = 0; i < n; ++i) {
62             scanf("%c ",&ch);
63             if (ch == ‘M‘) {
64                 scanf("%d%d",&a,&b);
65                 getchar();
66                 merg(a, b);
67             }
68             else {
69                 scanf("%d",&a);
70                 getchar();
71                 findset(a);
72                 printf("%d\n",un[a]);
73             }
74         }
75     }
76     return 0;
77 }