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

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

来源： <http://www.patest.cn/contests/pat-a-practise/1067>

 

#include <iostream>
#include <vector>
using namespace std;
vector<int> num;
int a[100010] = { 0 };
int main(void) {
	int n;
	cin >> n;
	for (int i = 0; i < n; i++) {
		int temp;
		cin >> temp;
		num.push_back(temp);
	}
	int count = 0;
	for (int i = 0; i < n; i++) {
		if (num[i] != i)
			count++;
		else
			a[i]++;
	}
	if (num[0] == 0)
		count++;
	count--;
	a[0] = 1;
	int j = 0, p = 0;
	int check = 0;
	bool flag = false;
	for (int q = 0; q < n; q++)
	{
		while (a[j] == 1) {
			j = num[j];
			a[j] ++;
		}
		if (a[q] == 0) {
				j = q;
				a[j] = 1;
				count++;
				continue;
		}
	}
	
	cout << count ;
	return 0;
}

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