Minimum Depth of Binary Tree leetcode java

题目

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.

 

题解

递归解法急速判断左右两边子树哪个depth最小,要注意如果有个节点只有一边孩子时,不能返回0,要返回另外一半边的depth。

递归解法:

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

 非递归解法:

 1     public int minDepth(TreeNode root) {
 2         if(root == null)
 3             return 0;
 4         
 5         int depth = 1;//The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.
 6         LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
 7         queue.add(root);
 8         int curnum = 1;
 9         int nextnum = 0;
10         while(!queue.isEmpty()){
11             TreeNode cur = queue.poll();
12             curnum--;
13             
14             if(cur.left == null && cur.right == null)
15                 return depth;
16             
17             if(cur.left != null){
18                queue.add(cur.left);
19                nextnum++;
20             }
21             
22             if(cur.right != null){
23                 queue.add(cur.right);
24                 nextnum++;
25             }
26             
27             if(curnum == 0){
28                 curnum = nextnum;
29                 nextnum = 0;
30                 depth++;
31             }
32         }
33         return depth;
34     }

 

posted @ 2014-07-31 00:47  爱做饭的小莹子  阅读(3145)  评论(0编辑  收藏  举报