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。

 #include <cstdio>
 #include <cstring>
 #include <iostream>
 #include <cmath>
 #include <algorithm>
 using namespace std;
 int p[];
 struct node
 {
     int id;
     int x;
     int pos;
 }num[];
 int flag[],minz;
 int cmp1(node a,node b)
 {
     return a.x < b.x;
 }
 int cmp2(node a,node b)
 {
     return a.id < b.id;
 }
 int judge(int x)
 {
     int res = ,m,temp = ;
     if(x == num[x].pos)
     {
         flag[x] = ;
         return ;
     }
     m = num[x].x;
     while(!flag[x])
     {
         flag[x] = ;
         temp += num[x].x;
         x = num[x].pos;
         m = min(m,num[x].x);
         res ++;
     }
     return temp + min((res-)*m,m+(res+)*minz);
 }
 int main()
 {
     int n,i,sum;
     scanf("%d",&n);
     minz = ;
     sum = ;
     for(i = ;i <= n;i ++)
     {
         scanf("%d",&num[i].x);
         minz = min(num[i].x,minz);
         num[i].id = i;
     }
     sort(num+,num+n+,cmp1);
     for(i = ;i <= n;i ++)
     {
         num[i].pos = i;
     }
     sort(num+,num+n+,cmp2);
     for(i = ;i <= n;i ++)
     {
         if(!flag[i])
         {
             sum += judge(i);
         }
     }
     printf("%d\n",sum);
     return ;
 }