迭代

class Solution {public int maxDepth(TreeNode root) {if(root==null){return 0;}int de=0;Queue<TreeNode> qu=new LinkedList<>();TreeNode tn;int le;qu.offer(root);while(!qu.isEmpty()){le=qu.size();while(le>0){tn=qu.poll();if(tn.left!=null){qu.offer(tn.left);}if(tn.right!=null){qu.offer(tn.right);}le--;}de++;}return de;}
}

class Solution(object):def maxDepth(self, root):if root is None:return 0de=0qu=collections.deque()qu.append(root)while qu:le=len(qu)while le>0:tn=qu.popleft()if tn.left:qu.append(tn.left)if tn.right:qu.append(tn.right)le-=1de+=1return de

递归

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

class Solution(object):def maxDepth(self, root):de=0nod=rootdef Explore(nod,de):if nod is None:return dede+=1return max(Explore(nod.left,de),Explore(nod.right,de))return Explore(root,de)