Cracking the Coding Interview

CountPairsOfIntegersThatHaveDifferenceK.java

import java.util.*;

class CountPairsOfIntegersThatHaveDifferenceK {
    
    static int f1(/*distinct*/final int[] A, final int K) {
        int count = 0;
        for (int i = 0; i < A.length - 1; i++) {
            for (int j = i + 1; j < A.length; j++) {
                if (Math.abs(A[j] - A[i]) == K) {
                    count++;
                }
            }
        }
        return count;
    }

    static int f2(final int[] A, final int K) {
	final Set<Integer> set = new HashSet<>();
	for (final int a : A) {
	    set.add(a);
	}
	int count = 0;
	for (final int a: A) {
	    if (set.contains(a + K)) {
		count++;
	    }
	}
	return count;
    }
    
    public static void main(final String... args) {
        if (args.length < 3) {
            return;
        }
        final int[] A = new int[args.length - 1];
        for (int i = 0; i < A.length; i++) {
            A[i] = Integer.parseInt(args[i]);
        }
        final int K = Integer.parseInt(args[args.length - 1]);
        System.out.println(f1(A, K));
	System.out.println(f2(A, K));
    }
}