Depth of Tree

1. Maximum Depth of Binary Tree

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.

Example

Given a binary tree as follow:

  1
 / \ 
2   3
   / \
  4   5

The maximum depth is 3.

Think

• Recursively check the depth
• Only if the node is a leaf node we stop recursion and return 0
• We compare the recursion results from left branch and right branch to get the maximum value.

Solution

public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: An integer.
     */
    public int maxDepth(TreeNode root) {
        if(root == null)
            return 0;
        int left = maxDepth(root.left);
        int right = maxDepth(root.right);
        return Math.max(left, right) + 1;
    }
}

2. Minimum Depth of Tree

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

Example

Given a binary tree as follow:

        1

     /     \ 

   2       3

          /    \

        4      5

The minimum depth is 2

Think

• Recursively check the depth
• Only if the node is a leaf node we stop recursion and return 0
• If a node just have one child, we should not compare the recursion result!
• If a node contains both left and right child, we compare the recursion results to get the minimum value.

Solution

public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: An integer.
     */
    public int minDepth(TreeNode root) {
        // write your code here
        if(root == null)
            return 0;

        if(root.left == null)
            return minDepth(root.right) + 1;
        else if(root.right == null)    
            return minDepth(root.left) + 1;
        else
            return Math.min(minDepth(root.left), minDepth(root.right)) + 1;
    }
}