【Hot100】LeetCode—104. 二叉树的最大深度

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• 原题连接：104. 二叉树的最大深度

1- 思路

队列——层序遍历

• 1- 借助队列实现层序遍历 Queue<TreeNode> queue = new LinkedList<>()
• 2- 遍历条件
  • while(!queue.isEmpty())

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2- 实现

⭐104. 二叉树的最大深度——题解思路

class Solution {List<Integer> res = new ArrayList<>();public int maxDepth(TreeNode root) {int depth = 0;if(root==null){return depth;}// 借助队列Queue<TreeNode> queue = new LinkedList<>();queue.offer(root);while(!queue.isEmpty()){int len = queue.size();// pathwhile(len>0){TreeNode nowNode = queue.poll();if(nowNode.left != null) queue.offer(nowNode.left);if(nowNode.right != null) queue.offer(nowNode.right);len--;}depth++;}return depth;}
}

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3- ACM 实现

public class maxDepth {public static class TreeNode {int val;TreeNode left;TreeNode right;TreeNode() {}TreeNode(int val) { this.val = val; }TreeNode(int val, TreeNode left, TreeNode right) {this.val = val;this.left = left;this.right = right;}}public static TreeNode build(String str){if(str == null || str.length()==0){return null;}String input = str.replace("[","");input = input.replace("]","");String[] parts = input.split(",");Integer[] nums = new Integer[parts.length];for(int i = 0 ; i < parts.length;i++){if(!parts[i].equals("null")){nums[i] = Integer.parseInt(parts[i]);}else{nums[i] = null;}}Queue<TreeNode> queue = new LinkedList<>();TreeNode root = new TreeNode(nums[0]);queue.offer(root);int index = 1;while(!queue.isEmpty()&& index<parts.length){TreeNode node = queue.poll();if(index<nums.length && nums[index]!=null){node.left = new TreeNode(nums[index]);queue.offer(node.left);}index++;if(index<nums.length && nums[index]!=null){node.right = new TreeNode(nums[index]);queue.offer(node.right);}index++;}return root;}public static int maxDepth(TreeNode root) {int depth = 0;if(root==null){return depth;}// 借助队列Queue<TreeNode> queue = new LinkedList<>();queue.offer(root);while(!queue.isEmpty()){int len = queue.size();// pathwhile(len>0){TreeNode nowNode = queue.poll();if(nowNode.left != null) queue.offer(nowNode.left);if(nowNode.right != null) queue.offer(nowNode.right);len--;}depth++;}return depth;}public static void main(String[] args) {Scanner sc = new Scanner(System.in);String input = sc.nextLine();TreeNode root = build(input);System.out.println("结果是"+maxDepth(root));}
}

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