Maximum Depth of Binary Tree leetcode java

題目：

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

 

題解：

遞迴解法：

     public int maxDepth(TreeNode root) {
2         if(root==null)
3             return 0;
4         int leftmax = maxDepth(root.left);
5         int rightmax = maxDepth(root.right);
6         return Math.max(leftmax, rightmax)+1;
7     }

 

 非遞迴解法，參考codeganker（http://codeganker.blogspot.com/2014/02/maximum-depth-of-binary-tree-leetcode.html）的：

 

 1 public int maxDepth(TreeNode root) {
 2     if(root == null)
 3         return 0;
 4     
 5     int depth = 0;
 6     LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
 7     queue.add(root);
 8     int curNum = 1; //num of nodes left in current level
 9     int nextNum = 0; //num of nodes in next level
10     while(!queue.isEmpty()){
11         TreeNode n = queue.poll();
12         curNum--;
13         if(n.left!=null){
14             queue.add(n.left);
15             nextNum++;
16         }
17         if(n.right!=null){
18             queue.add(n.right);
19             nextNum++;
20         }
21         if(curNum == 0){
22             curNum = nextNum;
23             nextNum = 0;
24             depth++;
25         }
26     }
27     return depth;
28 }