Solution.cpp

/**
 * 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:
    TreeNode* findNearestRightNode(TreeNode* root, TreeNode* u) {
        queue<TreeNode*> q{{root}};
        while (q.size()) {
            for (int i = q.size(); i; --i) {
                root = q.front();
                q.pop();
                if (root == u) return i > 1 ? q.front() : nullptr;
                if (root->left) q.push(root->left);
                if (root->right) q.push(root->right);
            }
        }
        return nullptr;
    }
};