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.
Recursion way is easy to think. Similar with "Minimum Depth of Binary Tree", time complexity is O(n).
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */ 10 public class Solution { 11 public int maxDepth(TreeNode root) { 12 if (root == null) 13 return 0; 14 return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1; 15 } 16 }
We can still use level order traversal to get depth.
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */ 10 public class Solution { 11 public int maxDepth(TreeNode root) { 12 if (root == null) 13 return 0; 14 List<TreeNode> current = new ArrayList<TreeNode>(); 15 current.add(root); 16 List<TreeNode> next; 17 int result = 1; 18 while (current.size() > 0) { 19 next = new ArrayList<TreeNode>(); 20 for (TreeNode tmpNode : current) { 21 if (tmpNode.left != null) 22 next.add(tmpNode.left); 23 if (tmpNode.right != null) 24 next.add(tmpNode.right); 25 } 26 current = next; 27 result++; 28 } 29 return result - 1; 30 } 31 }
Maximum Depth of Binary Tree 解答
原文：http://www.cnblogs.com/ireneyanglan/p/4834442.html