SPOJ IITKWPCO: Create Collections

This blog is intended to discuss many things of which algorithmic problems are a part.
So lets begin with a fairly simple problem Create Collections on spoj:
The problem can easily be solved by hashing as the constraints are really poor. By hashing, we can find out for each number whether a corresponding double number exists or not. Rest is simple :) Below is the accepted code for the problem:

	#include<iostream>
	#include<cstdio>
	#include<algorithm>
	#include<cstdlib>
	#include<cstring>
	using namespace std;
	int hash[10000000];
	int main()
	{
	int t, n, i, a[103], count;
	scanf("%d", &t);
	while(t--) {
	count=0;
	memset(hash, 0, sizeof(hash));
	scanf("%d", &n);
	for(i=0; i<n; i++) {
	scanf("%d", &a[i]);
	hash[a[i]]+=1;
	}
	sort(a, a+n);
	for(i=0; i<n; i++) {
	if(hash[a[i]]>0 && hash[2*a[i]]>0) {
	hash[a[i]]--;
	hash[2*a[i]]--;
	count++;
	}
	}
	printf("%d\n", count);
	}
	return 0;
	}

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