**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));
}
}

*Related*