Minimum Depth of Binary 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.

Note: A leaf is a node with no children.

 

Example 1:

Input: root = [3,9,20,null,null,15,7]

Output: 2

Example 2:

Input: root = [2,null,3,null,4,null,5,null,6]

Output: 5

 

Constraints:

The number of nodes in the tree is in the range [0, 105].

-1000 <= Node.val <= 1000

/**

 * 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 minDepth(TreeNode root) {

               if (root == null) return 0;

        // If left is null, go right

        if (root.left == null) return 1 + minDepth(root.right);

        // If right is null, go left

        if (root.right == null) return 1 + minDepth(root.left);

        // If both children exist, take the min of both

        return 1 + Math.min(minDepth(root.left), minDepth(root.right));

    }

}