LeetCode-in-Java

1424. Diagonal Traverse II

Medium

Given a 2D integer array nums, return all elements of nums in diagonal order as shown in the below images.

Example 1:

Input: nums = [[1,2,3],[4,5,6],[7,8,9]]

Output: [1,4,2,7,5,3,8,6,9]

Example 2:

Input: nums = [[1,2,3,4,5],[6,7],[8],[9,10,11],[12,13,14,15,16]]

Output: [1,6,2,8,7,3,9,4,12,10,5,13,11,14,15,16]

Constraints:

• 1 <= nums.length <= 105
• 1 <= nums[i].length <= 105
• 1 <= sum(nums[i].length) <= 105
• 1 <= nums[i][j] <= 105

Solution

import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Objects;

public class Solution {
    public int[] findDiagonalOrder(List<List<Integer>> nums) {
        List<Integer> ans = new ArrayList<>();
        ArrayDeque<Iterator<Integer>> queue = new ArrayDeque<>();
        int pos = 0;
        do {
            if (pos < nums.size()) {
                queue.offerFirst(nums.get(pos).iterator());
            }
            int sz = queue.size();
            while (--sz >= 0) {
                Iterator<Integer> cur = queue.poll();
                ans.add(Objects.requireNonNull(cur).next());
                if (cur.hasNext()) {
                    queue.offer(cur);
                }
            }
            pos++;
        } while (!queue.isEmpty() || pos < nums.size());
        return ans.stream().mapToInt(o -> o).toArray();
    }
}

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