Univalued Binary Tree

Problem

A binary tree is uni-valued if every node in the tree has the same value.

Given the root of a binary tree, return true if the given tree is uni-valued, or false otherwise.

Constraints

• The number of nodes in the tree is in the range [1, 100].
• 0 <= Node.val < 100

Solution

The problem Univalued Binary Tree can be solved using a depth-first search to compare all node values.

Implementation

static const int fast_io = []()
{
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    return 0;
}();

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution
{
  public:
    bool helper(TreeNode *root, int val)
    {
        if (root == NULL)
            return true;

        return root->val == val && helper(root->left, val) && helper(root->right, val);
    }

    bool isUnivalTree(TreeNode *root) { return helper(root, root->val); }
};