104. Maximum Depth of Binary Tree

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LeetCode

BFS

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/**
 * Definition for a binary tree node.
 * public 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;
 *     }
 * }
 */
class Solution {
    public int maxDepth(TreeNode root) {
        LinkedList<ArrayList<TreeNode>> queue=new LinkedList<>();
        int depth=0;
        if(root==null) return depth;
        queue.push(new ArrayList<>(Arrays.asList(root)));
        while(!queue.isEmpty()){
            ArrayList<TreeNode> tmp=queue.poll();
            ArrayList<TreeNode> tmpLs=new ArrayList<>();
            for(TreeNode i:tmp){              
                if(i.left!=null) tmpLs.add(i.left);
                if(i.right!=null) tmpLs.add(i.right);
            } 
            if(!tmpLs.isEmpty())queue.push(tmpLs);
            depth++;
        }
        return depth;
    }
}

Recursion

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class Solution {
    public int maxDepth(TreeNode root) {
        if(root==null) return 0;
        return Math.max(maxDepth(root.left),maxDepth(root.right))+1;
    }
}

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