PAT Advanced 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 (≤) 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

 

依旧采用柳神的办法（好精巧，不知道怎么想到的），柳太强了。

0号哨兵。第一位开始遍历，如果不与该位置相等，0号一直调整到相应位置，自己和0号位置交换。

#include <iostream>
#include <map>
#include <algorithm>
using namespace std;
int main() {
    int N, cnt = 0, tmp;
    scanf("%d", &N);
    map<int, int> m;
    for(int i = 0; i < N; i++){
        scanf("%d", &tmp);
        m[tmp] = i;
    }
    for(int i = 1; i < N; i++) {
        if(i != m[i]) {
            while(m[0] != 0) {
                swap(m[0], m[m[0]]);
                cnt++;
            }
            if(i != m[i]) {
                swap(m[0], m[i]);
                cnt++;
            }
        }
    }
    cout << cnt;
    system("pause");
    return 0;
}