POJ 3270 Cow Sorting(置换群)

题目链接

很早之前就看过这题，思路题把，确实挺难想的，黑书248页有讲解。

 1 #include <cstdio>

 2 #include <cstring>

 3 #include <iostream>

 4 #include <cmath>

 5 #include <algorithm>

 6 using namespace std;

 7 int p[10001];

 8 struct node

 9 {

10     int id;

11     int x;

12     int pos;

13 }num[10001];

14 int flag[10001],minz;

15 int cmp1(node a,node b)

16 {

17     return a.x < b.x;

18 }

19 int cmp2(node a,node b)

20 {

21     return a.id < b.id;

22 }

23 int judge(int x)

24 {

25     int res = 0,m,temp = 0;

26     if(x == num[x].pos)

27     {

28         flag[x] = 1;

29         return 0;

30     }

31     m = num[x].x;

32     while(!flag[x])

33     {

34         flag[x] = 1;

35         temp += num[x].x;

36         x = num[x].pos;

37         m = min(m,num[x].x);

38         res ++;

39     }

40     return temp + min((res-2)*m,m+(res+1)*minz);

41 }

42 int main()

43 {

44     int n,i,sum;

45     scanf("%d",&n);

46     minz = 100000000;

47     sum = 0;

48     for(i = 1;i <= n;i ++)

49     {

50         scanf("%d",&num[i].x);

51         minz = min(num[i].x,minz);

52         num[i].id = i;

53     }

54     sort(num+1,num+n+1,cmp1);

55     for(i = 1;i <= n;i ++)

56     {

57         num[i].pos = i;

58     }

59     sort(num+1,num+n+1,cmp2);

60     for(i = 1;i <= n;i ++)

61     {

62         if(!flag[i])

63         {

64             sum += judge(i);

65         }

66     }

67     printf("%d\n",sum);

68     return 0;

69 }