111. Minimum Depth of Binary Tree

https://www.youtube.com/watch?v=Knj-ViB96JM

 

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

 

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:

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

    3
   / \
  9  20
    /  \
   15   7

return its minimum depth = 2.