Find nearest right node in binary tree

Tree Breadth-First Search Binary Tree

75.1% acceptance

Mar 31, 2026

333

Given the root of a binary tree and a node u in the tree, return the nearest node on the same level that is to the right of u, or return null if u is the rightmost node in its level.

Solution

C++

Time O(n²)

Space O(1)

LeetCode

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;
    q.push(root);
    while (!q.empty()) {
      int sz = q.size();
      for (int i = 0; i < sz; i++) {
        TreeNode* node = q.front(); q.pop();
        if (node == u) {
          return (i < sz - 1) ? q.front() : nullptr;
        }
        if (node->left) q.push(node->left);
        if (node->right) q.push(node->right);
      }
    }
    return nullptr;
  }
};