InterviewStreet CouponDunia Count Pairs Problem: C++ code

CouponDunia Count Pairs Problem

Problem Statement

Given N numbers , [N<=10^5] we need to count the total pairs of numbers 

that have a difference of K. [K>0 and K<1e9]

Input Format:
1st line contains N & K (integers).
2nd line contains N numbers of the set. All the N numbers are assured 

to be distinct. 

Output Format:
One integer saying the no of pairs of numbers that have a diff K.

Sample Input #00:
5 2
1 5 3 4 2

Sample Output #00:
3 

Sample Input #01:
10 1
363374326 364147530 61825163 1073065718 1281246024 1399469912 428047635
491595254 879792181 1069262793

Sample Output #01:
0 

Solution

#include<iostream>
#include<algorithm>

using namespace std;
int compare (const void * a, const void * b)
{
  return ( *(int*)a - *(int*)b );
}

int main()
{
int n,k;

cin>>n>>k;
int a[n];
for(int i=0;i<n;i++)
cin>>a[i];

qsort(a,n,sizeof(int),compare);

int seq=0;
for(int i=0;i<n;i++)
{
int key=a[i]+k;
if(((int*)bsearch(&key,a+i+1,n-i-1,sizeof(int),compare))!=NULL)
seq++;
} 

cout<<seq;

}

Time Complexity : O(nlogn)