poj 1674 Sorting by Swapping 置换群

　若置换循环因子阶数分别为 ( a1, a2, ..., ak ) , 则最少交换次数为 (a1-1)+(a2-1)+...+(ak-1) 

解题代码

View Code

#include<stdio.h>

#include<string.h>

#include<stdlib.h>



const int N = 10010;



int a[N], n;

bool vis[N];



int check( int s )

{

    for(int i = s; i <= n; i++)

        if( !vis[i] ) return i;

    return -1;

}

int main()

{

    int T;

    scanf("%d", &T);

    while( T-- )

    {

        scanf("%d", &n);    

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

            scanf("%d", &a[i] );

        int res = 0, pos = 1;

        memset( vis, 0, sizeof(vis));

        while( (pos=check(pos)) != -1 )

        {

            int s = pos, cnt = 0;

            while( !vis[s] )

            {

                vis[s] = true;

                cnt++;

                s = a[s];

            }

            res += cnt-1;    

        }

        printf("%d\n", res );    

    }

    return 0;

}