题目描述

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

代码

#include <iostream>
using namespace std;
int main() {
    int n, t, cnt = 0, a[100010];
    cin >> n;
    for (int i = 0; i < n; i++) {
        cin >> t;
        a[t] = i;
    }
    for (int i = 1; i < n; i++) {
        if (i != a[i]) {
            while (a[0] != 0) {
                swap(a[0], a[a[0]]);
                cnt++;
            }
            if (i != a[i]) {
                swap(a[0], a[i]);
                cnt++;
            }
        }
    }
    cout << cnt;
    return 0;
}