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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 (≤105) 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;
}