111.二叉树的最小与最大深度

题目链接：https://leetcode-cn.com/problems/minimum-depth-of-binary-tree/

解题思路：

都是层次遍历，判断返回的条件不一样。

 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 class Solution {
11     public int minDepth(TreeNode root) {
12         
13         ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
14         ArrayList<Integer> list = new ArrayList<>();
15         ArrayList<TreeNode> queue = new ArrayList<>();
16         
17         if(root==null)
18             return 0;
19         
20         int start = 0;
21         int end = 1;
22         queue.add(root);
23         int count=1;
24         while(!queue.isEmpty())
25         {
26             TreeNode node = queue.remove(0);
27             start++;
28             if(node.left==null&&node.right==null)
29                 break;
30             if(node.left!=null)
31                 queue.add(node.left);
32             if(node.right!=null)
33                 queue.add(node.right);
34             
35             
36             list.add(node.val);
37             if(start == end)
38             {
39                 res.add(list);
40                 count++;
41                 start = 0;
42                 end = queue.size();
43                 list = new ArrayList<>();
44             }
45         }
46         return count;
47         
48     }
49 }

 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 class Solution {
11     public int maxDepth(TreeNode root) {
12         
13         ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
14         ArrayList<Integer> list = new ArrayList<>();
15         ArrayList<TreeNode> queue = new ArrayList<>();
16         
17         if(root==null)
18             return 0;
19         
20         int start = 0;
21         int end = 1;
22         queue.add(root);
23         int count=0;
24         while(!queue.isEmpty())
25         {
26             TreeNode node = queue.remove(0);
27             start++;
28             if(node.left!=null)
29                 queue.add(node.left);
30             if(node.right!=null)
31                 queue.add(node.right);
32             list.add(node.val);
33             if(start == end)
34             {
35                 res.add(list);
36                 count++;
37                 start = 0;
38                 end = queue.size();
39                 list = new ArrayList<>();
40             }
41         }
42         return count;
43         
44     }
45 }

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    int result = 0;//最大深度
    public int maxDepth(TreeNode root) {
        
        if (root == null) {
            return 0;
        }
        result = Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
        return result;
        
    }
}