LeetCode-Find K Pairs with Smallest Sums

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:

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

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

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:

Given nums1 = [1,1,2], nums2 = [1,2,3],  k = 2

Return: [1,1],[1,1]

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:

Given nums1 = [1,2], nums2 = [3],  k = 3 

Return: [1,3],[2,3]

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

Credits:
Special thanks to @elmirap and @StefanPochmann for adding this problem and creating all test cases.

 

Solution:

 1 public class Solution {
 2     public List<int[]> kSmallestPairs(int[] nums1, int[] nums2, int k) {
 3         List<int[]> res = new ArrayList<int[]>();
 4     
 5     // corner case
 6     if (nums1.length == 0 || nums2.length == 0) return res;
 7     
 8     // priority queue comparing the pair sum
 9     PriorityQueue<int[]> pairs = new PriorityQueue<int[]>(
10         new Comparator<int[]>() {
11             public int compare(int[] v1, int[] v2){
12                 return (v1[0] - v2[0]);
13             }
14         });
15     
16     // for each num in nums1, increase the position in nums2 from 0
17     for (int i = 0; i < nums1.length; i++) {
18         int[] v = {nums1[i] + nums2[0], i, 0};
19         pairs.add(v);
20     }
21     
22     while (!pairs.isEmpty() && k > 0) {
23         int[] v = pairs.poll();
24         // move to the next position in nums2
25         if (v[2] < nums2.length - 1)    {
26             int[] nv = {nums1[v[1]] + nums2[v[2] + 1], v[1], v[2] + 1};
27             pairs.add(nv);
28         }
29         int[] pair = {nums1[v[1]], nums2[v[2]]};
30         res.add(pair);
31         
32         k--;
33     }
34     
35     return res;
36     }
37 }

 

posted @ 2016-07-18 14:48  LiBlog  阅读(122)  评论(0)  编辑  收藏  举报