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 }