1224. Exchange bottles

Idea 1:
Violence

Code:

# include<iostream>
# include<cstdio>
# include<cstring>
# include<algorithm>
using namespace std;

const int N = 10010;
int a[N];
int cnt,n;

int main()
{
    
    
    cin >> n;
    for(int i = 1;i <= n;i++)
    {
    
    
        scanf("%d",&a[i]);
    }
    for(int i = 1;i <= n;i++)
    {
    
    
        while(i != a[i])
        {
    
    
            swap(a[i],a[a[i]]);
            cnt++;
        }
    }
    printf("%d\n",cnt);
    return 0;
}

Idea 2:
Use the operating code of the ring





:

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
const int N=1e5+5;
int a[N];
bool st[N];
int main(){
    
    
    int n;
    cin >> n;
    for(int i=1;i<=n;i++){
    
    
        cin >> a[i];
    }
    int cnt=0;
    for(int i=1;i<=n;i++){
    
    
        if(!st[i]){
    
    
            cnt++;
            for(int j=i;!st[j];j=a[j]){
    
    //位置j指向a[j]的元素
                st[j]=true;
            }
        }
    }
    cout << n-cnt;
}