[刷题]Binary Tree Zigzag Level Order Traversal

最新推荐文章于 2024-08-23 15:23:16 发布

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本文介绍了如何使用广度优先搜索（BFS）算法来解决二叉树的锯齿形层次遍历问题，提供了一个简洁且高效的解决方案。

[LintCode]Binary Tree Zigzag Level Order Traversal

/**
 * 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: A list of lists of integer include 
     *          the zigzag level order traversal of its nodes' values 
     */
    public ArrayList<ArrayList<Integer>> zigzagLevelOrder(TreeNode root) {
        // 2015-3-26 BFS
        ArrayList<ArrayList<Integer>> rst = new ArrayList<>();
        if (root == null) {
            return rst;
        }
        
        int count = 0;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        
        while (!queue.isEmpty()) {
            ArrayList<Integer> level = new ArrayList<>();
            count++;
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode temp = queue.poll();
                if (count % 2 == 1) {
                    level.add(temp.val);
                } else {
                    level.add(0, temp.val);
                }
                if (temp.left != null) {
                    queue.offer(temp.left);
                }
                if (temp.right != null) {
                    queue.offer(temp.right);
                }
            }
            rst.add(level);
        }
        return rst;
    }
}