**Problem:**

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.

**Solution:**

DFS

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

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