[LintCode] K-diff Pairs in an Array

Problem

Given an array of integers and an integer k, you need to find the number of unique k-diff pairs in the array. Here a k-diff pair is defined as an integer pair (i, j), where i and j are both numbers in the array and their absolute difference is k.

Example

Example 1:

Input: [3, 1, 4, 1, 5], k = 2
Output: 2
Explanation: There are two 2-diff pairs in the array, (1, 3) and (3, 5).
Although we have two 1s in the input, we should only return the number of unique pairs.
Example 2:

Input:[1, 2, 3, 4, 5], k = 1
Output: 4
Explanation: There are four 1-diff pairs in the array, (1, 2), (2, 3), (3, 4) and (4, 5).
Example 3:

Input: [1, 3, 1, 5, 4], k = 0
Output: 1
Explanation: There is one 0-diff pair in the array, (1, 1).

Solution

public class Solution {
    /**
     * @param nums: an array of integers
     * @param k: an integer
     * @return: the number of unique k-diff pairs
     */
    public int findPairs(int[] nums, int k) {
        //it actually wants unique pairs, so need to sort and leave out the duplicates
        Arrays.sort(nums);
        int count = 0;
        for (int i = 0; i < nums.length-1; i++) {
            if (i != 0 && nums[i] == nums[i-1]) continue;
            for (int j = i+1; j < nums.length; j++) {
                if (j != i+1 && nums[j] == nums[j-1]) continue;
                if (nums[j] - nums[i] == k) count++;
            }
        }
        return count;
    }
}