LeetCode 965. Univalued Binary Tree C 语言解法

965. Univalued Binary Tree

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.

示例 1

Input: root = [1,1,1,1,1,null,1]
Output: true

示例 2

Input: root = [2,2,2,5,2]
Output: false

约束条件

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

解题思路

• A tree is univalued if all nodes have the same value.
• Store the root's value as the target value.
• Use DFS (recursion):
  • If a node is NULL, return true.
  • If a node's value ≠ target → not univalued, return false.
  • Recursively check left and right children.
• If all nodes match the target value, return true.

代码实现

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *   int val;
 *   struct TreeNode *left;
 *   struct TreeNode *right;
 * };
 */
bool dfs(struct TreeNode* root, int target) {
    if (!root) return true;
    if (root->val != target) return ;
     dfs(root->left, target) && dfs(root->right, target);
}

  {
     dfs(root, root->val);
}