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 = 0; i < arrays.length; i++) {
            if (arrays[i].length != 0) {
                minHeap.offer(new Record(i, 0, arrays[i][0]));
            }
        }

        List<Integer> result = new ArrayList<>();
        while (!minHeap.isEmpty()) {
            Record record = minHeap.poll();
            result.add(record.val);
            if (record.col + 1 < arrays[record.row].length) {
                minHeap.offer(new Record(record.row, record.col + 1, arrays[record.row][record.col + 1]));
            }
        }
        return result;
    }
}