### Find Minimum Depth of Binary Tree - The Coding Shala

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## Find 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:

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

3

/ \

9 20

/ \

15 7

return its minimum depth = 2.

### Find Minimum Depth of Binary Tree Java Program

**Method 1:**

Using recursion.

Java Code:

/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { public int minDepth(TreeNode root) { if(root==null) return 0; if(root.left==null) return 1+minDepth(root.right); if(root.right==null) return 1+minDepth(root.left); return 1+Math.min(minDepth(root.left), minDepth(root.right)); } }

**Method 2:**

Using level order traversal.

We do level-order traversal and increase depth according to the current level when meeting a node in which both children is null then return the depth.

Java Code:

/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { public int minDepth(TreeNode root) { if(root==null) return 0; int depth = 1; Queue<TreeNode> queue = new LinkedList<TreeNode>(); queue.offer(root); while(!queue.isEmpty()){ int size = queue.size(); for(int i=0;i<size;i++){ TreeNode curr = queue.poll(); if(curr.left==null && curr.right==null) return depth; if(curr.left!=null) queue.offer(curr.left); if(curr.right!=null) queue.offer(curr.right); } depth++; } return depth; } }

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