Minimum Depth of Binary Tree

题目：

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.

 

题解： 

递归解法急速判断左右两边子树哪个depth最小，要注意如果有个节点只有一边孩子时，不能返回0，要返回另外一半边的depth。 

递归解法：

 1 public class Solution {
 2     public int minDepth(TreeNode root) 
 3     {
 4         int depth=0;
 5         depth=depthHelper(root,depth);
 6         return depth;
 7     }
 8     
 9     public int depthHelper(TreeNode root, int depth)
10     {
11         if(root==null)
12         return 0;
13         
14         depth+=1;
15         if(root.left!=null&&root.right!=null) 
16         {
17            return Math.min(depthHelper(root.left,depth),depthHelper(root.right,depth));
18         }
19         else if (root.left==null&&root.right!=null)
20         {
21             return depthHelper(root.right,depth);
22         }
23         else if(root.left!=null&&root.right==null)
24         {
25             return depthHelper(root.left,depth);
26         }
27         else return depth;
28 
29     }
30 }

 

解法二：

public class Solution {
    public int minDepth(TreeNode root) {
        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;
    }
}

 

posted @ 2015-08-05 06:27  Hygeia  阅读(156)  评论(0)  编辑  收藏  举报