Leetcode: Minimum Depth of Binary Tree

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.

1 public int minDepth(TreeNode root) {
2     if(root == null)
3         return 0;
4     if(root.left == null)
5         return minDepth(root.right)+1;
6     if(root.right == null)
7         return minDepth(root.left)+1;
8     return Math.min(minDepth(root.left),minDepth(root.right))+1;
9 }

 1 public int minDepth(TreeNode root) {
 2     if(root == null)
 3         return 0;
 4     LinkedList queue = new LinkedList();
 5     int curNum = 0;
 6     int lastNum = 1;
 7     int level = 1;
 8     queue.offer(root);
 9     while(!queue.isEmpty())
10     {
11         TreeNode cur = queue.poll();
12         if(cur.left==null && cur.right==null)
13             return level;
14         lastNum--;
15         if(cur.left!=null)
16         {
17             queue.offer(cur.left);
18             curNum++;
19         }
20         if(cur.right!=null)
21         {
22             queue.offer(cur.right);
23             curNum++;
24         }
25         if(lastNum==0)
26         {
27             lastNum = curNum;
28             curNum = 0;
29             level++;
30         }
31     }
32     return 0;
33 }