PAT.A1067. Sort with Swap(0,*)

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

有2个点需要注意，数据录入的时候要直接记录数据的位置，不要按顺序录入数据，其次是搜索不在本位的数据时不要每次都从头搜索，不然一定会超时。

#include <cstdio>
#include <cstring>
#include <string>
#include <algorithm>
#include <cmath>
#include <map>
using namespace std;
int a[100010];
int main(){
	int n,count=0,j=1,num;
	bool f=1;
	scanf("%d", &n);
	for (int i = 0; i < n; i++) {
		scanf("%d", &num);
		a[num] = i;
	}
	while(f) {
		f = 0;
		if (a[0] != 0) {
			swap(a[0],a[a[0]] );
			count++;
			f = 1;
		}
		else {
			while(j<n) {
				if (a[j] != j) {
					swap(a[0], a[j]);
					count++;
					f = 1;
					break;
				}
				j++;
			}
		}
	}
	printf("%d", count);
	return 0;
	
}