lintcode155- Minimum Depth of Binary Tree- easy

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.

 Example

Given a binary tree as follow:

  1
 /  
2   3
   / 
  4   5

The minimum depth is 2.

分治法来做，返回左右小的深度+1。

1.注意处理一侧子树为空的情况，不能就断言最短深度是1了，因为定义要求你一定要下到叶子节点。

/**
 * 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;
        }
        
        int left = minDepth(root.left);
        int right = minDepth(root.right);
        
        // 切记处理一侧为空的情况，因为定义一定要走到叶子节点，所以此时不能就返回min = 1。以下处理即把0的那个排除掉。
        if (left == 0 || right == 0) {
            return 1 + Math.max(left, right);
        }
        
        return 1 + Math.min(left, right);
    }
}