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.

意思就是求一個二叉樹的最短路徑(￣▽￣)"

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