【1对】Univalued Binary Tree

https://leetcode.com/problems/univalued-binary-tree/

日期	是否一次通过	comment
2019-01-16 19:27	一次通过	本质是preOrder

image.png

（来源： https://leetcode.com/problems/univalued-binary-tree/）

本质上就是个遍历啊

递归

class Solution {
    public boolean isUnivalTree(TreeNode root) {
        if(root == null) {
            return true;
        }
        
        int[] tempNum = new int[]{root.val};
        
        return helper(root, tempNum);
    }
    
    private boolean helper(TreeNode root, int[] tempNum) {
        if(root == null) {
            return true;
        }
        
        if(root.val != tempNum[0]) {
            return false;
        }
        
        return helper(root.left, tempNum) && helper(root.right, tempNum);
    }
}

非递归

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