PAT-A-1067. Sort with Swap(0,*) (25)

1067. Sort with Swap(0,*) (25)

时间限制

150 ms

内存限制

65536 kB

代码长度限制

16000 B

判题程序

Standard

作者

CHEN, Yue

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<iostream>#include<cstdio>#include<algorithm>using namespace std;int pos[100010];int main(){  int n;  int num;  int left, ans=0;  cin >> n;  left = n-1;  for (int i = 0; i < n; i++)  {    cin >> num;    pos[num] = i;    if (num == i&&i != 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--;    }  }  cout << ans << endl;  system("pause");  return 0;}