[LeetCode] Problem 373 - Find K Pairs with Smallest Sums

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You are given two integer arrays nums1 and nums2 sorted in ascending order and an integer k.

Define a pair (u,v) which consists of one element from the first array and one element from the second array.

Find the k pairs (u1,v1),(u2,v2) …(uk,vk) with the smallest sums.

Example

No.1

Input: nums1 = [1,7,11], nums2 = [2,4,6], k = 3

Output: [[1,2],[1,4],[1,6]]

Explanation: The first 3 pairs are returned from the sequence:
[1,2],[1,4],[1,6],[7,2],[7,4],[11,2],[7,6],[11,4],[11,6]

No.2

Input: nums1 = [1,1,2], nums2 = [1,2,3], k = 2

Output: [1,1],[1,1]

Explanation: The first 2 pairs are returned from the sequence:
[1,1],[1,1],[1,2],[2,1],[1,2],[2,2],[1,3],[1,3],[2,3]

No.3

Input: nums1 = [1,2], nums2 = [3], k = 3

Output: [1,3],[2,3]

Explanation: All possible pairs are returned from the sequence: [1,3],[2,3]

Code

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public List<int[]> kSmallestPairs(int[] nums1, int[] nums2, int k) {
    List<int[]> result = new ArrayList<>();
    
    if (nums1.length == 0 || nums2.length == 0)
        return result;
    
    PriorityQueue<int[]> minHeap = new PriorityQueue<>(new Comparator<int[]>() {
        @Override
        public int compare(int[] o1, int[] o2) {
            return (o1[0] + o1[1]) - (o2[0] + o2[1]);
        }
    });

    for (int i = 0; i < Math.min(k, nums1.length); i++)
        minHeap.offer(new int[] {nums1[i], nums2[0], 0});

    while (!minHeap.isEmpty() && k > 0) {
        int[] pair = minHeap.poll();
        result.add(new int[] {pair[0], pair[1]});
        k--;
        
        if (pair[2] < nums2.length - 1)
            minHeap.offer(new int[] {pair[0], nums2[pair[2] + 1], pair[2] + 1});
    }

    return result;
}