Maximum Depth of Binary Tree

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.

 

非递归实现： 用ArrayList来实现层次遍历，用cnt和index来记录每层节点数目

java代码：

1. public int maxDepth(TreeNode root) {
2. if(root==null) return 0;
3. ArrayList<TreeNode> al = new ArrayList<TreeNode>();
4. TreeNode tmp;
5. int index=0;
6. int level=1;
7. int i=0; // the start
8. al.add(root);
9. index++; // the end
10. int cnt=1; // the number
11. while(cnt>0) {
12. cnt=0;
13. while(i<index) {
14. tmp=al.get(i);
15. if(tmp.left!=null) {
16. al.add(tmp.left);
17. cnt++;
18. }
19. if(tmp.right!=null) {
20. al.add(tmp.right);
21. cnt++;
22. }
23. i++;
24. }
25. index=index+cnt;
26. if(cnt!=0) level++;
27. }
28. return level;
29. }

递归：

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