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LeetCode

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Problem

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 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]

Example 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]

Example 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

class Solution {
    public List<List<Integer>> kSmallestPairs(int[] nums1, int[] nums2, int k) {
        List<List<Integer>> res = new ArrayList<>();
        if(nums1.length == 0 || nums2.length == 0 || k == 0) return res;

        PriorityQueue<int[]> pq = new PriorityQueue<>((a, b) -> (a[0] + a[1] - b[0] - b[1]));

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

        while (!pq.isEmpty() && k-- > 0) {
            int[] curr = pq.poll();
            res.add(Arrays.asList(curr[0], curr[1]));

            if(curr[2] == nums2.length - 1) continue;
            pq.offer(new int[]{curr[0], nums2[curr[2] + 1], curr[2] + 1});
        }

        return res;
    }
}