2. 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, 104].
• -1000 <= Node.val <= 1000

Solution:

class Solution {
 public int minDepth(TreeNode root) {
 
 if(root == null)
 return 0;
 
 if(root.left == null && root.right == null){
 return 1;
 } 
 
 int left = root.left != null ? minDepth(root.left) : Integer.MAX_VALUE;
 int right = root.right != null ? minDepth(root.right) : Integer.MAX_VALUE;
 
 return 1+Math.min(left,right);
 }
}