为啥数组前两位是零啊求大佬解答

#include<bits/stdc++.h>
using namespace std;

int a[1010],b[10101];

void ksort (int arr[],int l,int r)
{
	if (l >= r) return;
	int mid = (l + r) / 2;
	swap(arr[l],arr[mid]);
	
	int i = l + 1,j = r;
	
	while (i <= j) {
		while (i <= j && arr[i] < arr[l]) i++;
		while (i <= j && arr[j] > arr[l]) j--;
		if (i <= j)
		{
			swap (arr[i],arr[j]);
			i++,j--;
		}
	}
	swap(arr[l],arr[j]);
	ksort(arr,l,j - 1);
	ksort(arr,j + 1,r);
}
int main()
{
	int n,x,sum = 0;
	cin >> n;
	for (int i = 1;i <= n;i++) {
		cin >> x;
		a[x] = 1;
	}
	for (int i = 1;i <= 1001;i++) {
		if (a[i] == 1) {
			sum++;
			b[sum] = i;
		}
	}
	cout << sum << endl;
	ksort(b,1,n);
	for (int i = 1;i <= sum;i++) {
		cout << b[i] << " ";
	}
	return 0;
}