965. 单值二叉树

╰半橙微兮° 2023-02-18 03:01 60阅读 0赞

# 题目来源 #

[leetcode][]

# 题目描述 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg_size_16_color_FFFFFF_t_70]

# 题目解析 #

## 使用辅助栈 ##

class Solution {
        
        public boolean isUnivalTree(TreeNode root) {
        
            if (root == null){
        
                return true;
            }
            
            int val = root.val;
            Stack<TreeNode> stack = new Stack<>();
            stack.push(root);
            while (!stack.empty()){
        
                TreeNode treeNode = stack.pop();
                if (treeNode.val != val){
        
                    return false;
                }
                
                if (treeNode.left != null){
        
                    stack.push(treeNode.left);
                }
                
                if (treeNode.right != null){
        
                    stack.push(treeNode.right);
                }
            }
            
            return true;
        }
    }

![在这里插入图片描述][2020061515042457.png]

## 使用递归 ##

class Solution {
        
        public boolean isUnivalTree(TreeNode root) {
        
            if (root == null){
        
                return true;
            }
    
            int val = root.val;
            
            return helper(root, val);
        }
    
        private static boolean helper(TreeNode root, int val){
        
            if (root == null){
        
                return true;
            }
            
            if (root.val != val){
        
                return false;
            }
            
            boolean flag = helper(root.left, val);
            if (flag){
        
                flag = helper(root.right, val);
            }
            return flag;
        }
    
    }

![在这里插入图片描述][20200615150805476.png]

class Solution {
        
        public boolean isUnivalTree(TreeNode root) {
        
            if (root == null){
        
                return true;
            }
    
            int val = root.val;
            if (root.left != null && root.left.val != root.val){
        
                return false;
            }
    
            if (root.right != null && root.right.val != root.val){
        
                return false;
            }
    
            return isUnivalTree(root.left) && isUnivalTree(root.right);
        }
    }

![在这里插入图片描述][20200615151127145.png]

[leetcode]: https://leetcode-cn.com/problems/univalued-binary-tree/
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200615151212176.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg==,size_16,color_FFFFFF,t_70
[2020061515042457.png]: https://img-blog.csdnimg.cn/2020061515042457.png
[20200615150805476.png]: https://img-blog.csdnimg.cn/20200615150805476.png
[20200615151127145.png]: https://img-blog.csdnimg.cn/20200615151127145.png