lintcode-easy-Minimum Depth of Binary Tree

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.

Given a binary tree as follow:

  1
 / \ 
2   3
   / \
  4   5

The minimum depth is 2.

 

递归，注意定义，深度是指root到leaf node最短路径的节点个数，递归的基本情况是root为leaf node，而不是root为null。当然也要加入root为null时候的判断条件。

/**
 * 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;
        
        if(root.left == null && root.right == null)
            return 1;
        
        int left = Integer.MAX_VALUE;
        int right = Integer.MAX_VALUE;
        
        if(root.left != null)
            left = minDepth(root.left);
        if(root.right != null)
            right = minDepth(root.right);
        
        return Math.min(left, right) + 1;
    }
}