/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: An integer.
     */
    public int minDepth(TreeNode root) {
        // write your code here
        if (root == null) {
            return 0;
        }
        return getMin(root);
    }
    public int getMin(TreeNode root){
        if (root == null) {
            return Integer.MAX_VALUE;
        }

        if (root.left == null && root.right == null) {
            return 1;
        }

        return Math.min(getMin(root.left), getMin(root.right)) + 1;
    }
}

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: An integer.
     */
    public int minDepth(TreeNode root) {
        if(null == root) return 0;
        if(null == root.left) return minDepth(root.right) + 1;
        if(null == root.right) return minDepth(root.left) + 1;
        return Math.min(minDepth(root.left),minDepth(root.right)) + 1;
    }
    
}