题目地址

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

//此题不会
#include <string.h>
#include <stdio.h>
#include <algorithm>
using namespace std;
int main()
{
    int pos[100010],n,ans=0,left,num;
    scanf("%d",&n);
    left=n-1;
    for(int i=0;i<n;i++){
        scanf("%d",&num);
        pos[num]=i;
        if(num==i&&num!=0) left--;
    }
    int k=0;
    while(left>0){
        if(pos[0]==0){        //把零移到非pos[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;
}