[刷题]Binary Tree Level Order Traversal

最新推荐文章于 2024-08-23 15:23:16 发布

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本文介绍了一种解决二叉树层次遍历问题的方法。通过使用队列进行广度优先搜索（BFS），实现了对二叉树节点按层级顺序访问的功能，并返回每一层节点值组成的列表。

[LintCode]Binary Tree Level Order Traversal

答案

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
 
 
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Level order a list of lists of integer
     */
    public ArrayList<ArrayList<Integer>> levelOrder(TreeNode root) {
        // 2015-3-22 BFS
        ArrayList<ArrayList<Integer>> rst = new ArrayList<>();
        if (root == null) {
            return rst;
        }
        
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            ArrayList<Integer> level = new ArrayList<>();
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode temp = queue.poll();
                level.add(temp.val);
                if (temp.left != null) {
                    queue.offer(temp.left);
                }
                if (temp.right != null) {
                    queue.offer(temp.right);
                }
            }
            rst.add(level);
        }
        return rst;
        
    }
}