Maximum Depth of Binary Tree leetcode java

题目：

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.

 

题解：

递归解法：

1      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     }

 

 非递归解法，参考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 }