Merge K Sorted Arrays

This problem can be solved by using a heap. The time is O(nlog(n)).

Given m arrays, the minimum elements of all arrays can form a heap. It takes O(log(m)) to insert an element to the heap and it takes O(log(m)) to delete the minimum element.

 class Record {
     int row;
     int col;
     int val;

     public Record(int row, int col, int val) {
         this.row = row;
         this.col = col;
         this.val = val;
     }
 }

 public class Solution {
     public List<Integer> mergekSortedArrays(int[][] arrays) {
         PriorityQueue<Record> minHeap = new PriorityQueue<>((x, y) -> x.val - y.val);
         for (int i = ; i < arrays.length; i++) {
             if (arrays[i].length != ) {
                 minHeap.offer(new Record(i, , arrays[i][]));
             }
         }

         List<Integer> result = new ArrayList<>();
         while (!minHeap.isEmpty()) {
             Record record = minHeap.poll();
             result.add(record.val);
             if (record.col +  < arrays[record.row].length) {
                 minHeap.offer(new Record(record.row, record.col + , arrays[record.row][record.col + ]));
             }
         }
         return result;
     }
 }