Leetcode-102、二叉树的层序遍历

题解

Java题解
迭代

class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> res = new ArrayList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        if (root == null) {             // []
            return res;
        }
        queue.offer(root);
        while (!queue.isEmpty()) {        // 
            int size = queue.size();
            List<Integer> cur = new ArrayList<>();
            while (size != 0) {
                TreeNode tmp = queue.poll();
                cur.add(tmp.val);
                if (tmp.left != null) {
                    queue.offer(tmp.left);
                }
                if (tmp.right != null) {
                    queue.offer(tmp.right);
                }
                size -= 1;
            }
            res.add(cur);
        }
        return res;
    }
}

结果

image.png

测试数据

容易漏掉
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