1067 Sort with Swap(0, i) (25 分)

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1067 Sort with Swap(0, i) (25 分)

Given any permutation of the numbers {0, 1, 2,..., N−1}, it is easy to sort them in increasing order. But what if Swap(0, *) is the ONLY operation that is allowed to use? For example, to sort {4, 0, 2, 1, 3} we may apply the swap operations in the following way:

Swap(0, 1) => {4, 1, 2, 0, 3}
Swap(0, 3) => {4, 1, 2, 3, 0}
Swap(0, 4) => {0, 1, 2, 3, 4}

Now you are asked to find the minimum number of swaps need to sort the given permutation of the first N nonnegative integers.

Input Specification:

Each input file contains one test case, which gives a positive N (≤10​5​​) followed by a permutation sequence of {0, 1, ..., N−1}. All the numbers in a line are separated by a space.

Output Specification:

For each case, simply print in a line the minimum number of swaps need to sort the given permutation.

Sample Input:

10
3 5 7 2 6 4 9 0 8 1

Sample Output:

9

#include <bits/stdc++.h>
using namespace std;
const int maxn=100010;
int pos[maxn];

int main()
{
    int n,ans=0;
    scanf("%d",&n);
    int left=n-1;
    for(int i=0; i<n; i++)
    {
        int x;
        scanf("%d",&x);
        pos[x]=i;
        if(x==i&&x!=0)
        {
            left--;
        }
    }
    int k=1;
    while(left>0)
    {
        if(pos[0]==0)
        {
            while(k<n)
            {
                if(pos[k]!=k)
                {
                    swap(pos[0],pos[k]);
                    ans++;
                    break;
                }
                k++;
            }
        }
        while(pos[0]!=0)
        {
            swap(pos[0],pos[pos[0]]);
            ans++;
            left--;
        }
    }
    printf("%d\n",ans);
    return 0;
}