剑指 Offer 32. 从上到下打印二叉树 #

public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}

class Solution {
    public int[] levelOrder(TreeNode root) {
        List<Integer> ans = new ArrayList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        if (root != null) queue.offer(root);
        while (queue.size() != 0) {
            int layerSize = queue.size();
            for (int i = 0; i < layerSize; i++) {
                TreeNode node = queue.poll();
                ans.add(node.val);
                if (node.left != null) queue.offer(node.left);
                if (node.right != null) queue.offer(node.right);
            }
        }
        int[] result = new int[ans.size()];
        for (int i = 0; i < ans.size(); i++) result[i] = ans.get(i);
        return result;
    }
}