# Maximum Depth of Binary Tree

`Tree`, `BFS`, `DFS`

Easy

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree`[3,9,20,null,null,15,7]`,

``````    3
/ \
9  20
/  \
15   7
``````

return its depth = 3.

## Solution

#### *Recursive

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

#### DFS

``````public int maxDepth(TreeNode root) {
if(root == null) {
return 0;
}

Stack<TreeNode> stack = new Stack<>();
Stack<Integer> value = new Stack<>();
stack.push(root);
value.push(1);
int max = 0;
while(!stack.isEmpty()) {
TreeNode node = stack.pop();
int temp = value.pop();
max = Math.max(temp, max);
if(node.left != null) {
stack.push(node.left);
value.push(temp+1);
}
if(node.right != null) {
stack.push(node.right);
value.push(temp+1);
}
}
return max;
}
``````

#### *BFS

``````public int maxDepth(TreeNode root) {
if(root == null) {
return 0;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
int count = 0;
while(!queue.isEmpty()) {
int size = queue.size();
while(size-- > 0) {
TreeNode node = queue.poll();
if(node.left != null) {
queue.offer(node.left);
}
if(node.right != null) {
queue.offer(node.right);
}
}
count++;
}
return count;
}
``````