CountNDistinctPairsWithDifferenceK.java

package com.interview.binarysearch;

import java.util.Arrays;

/**
 * http://www.geeksforgeeks.org/count-pairs-difference-equal-k/
 */
public class CountNDistinctPairsWithDifferenceK {

    public int count(int arr[],int k){
        Arrays.sort(arr);
        int count = 0;
        for(int i=0; i < arr.length; i++){
            boolean result = binarySearch(arr, i+1, arr.length-1, arr[i] + k);
            if(result){
                count++;
            }
        }
        return count;
    }
    
    private boolean binarySearch(int arr[],int start,int end,int num){
        if(start > end){
            return false;
        }
        int mid = (start + end)/2;
        if(arr[mid] == num){
            return true;
        }
        else if(arr[mid] > num){
            return binarySearch(arr,start,mid-1,num);
        }else{
            return binarySearch(arr,mid+1,end,num);
        }
    }
    
    public static void main(String args[]){
        CountNDistinctPairsWithDifferenceK cn = new CountNDistinctPairsWithDifferenceK();
        int arr[] = {1,2,3,4,5,7,9};
        System.out.print(cn.count(arr, 3));
    }
}