Populating next right pointers in each node ii

Linked List Tree Depth-First Search Breadth-First Search Binary Tree

57.2% acceptance

Jan 13, 2026

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Given a binary tree struct Node { int val; Node *left; Node *right; Node *next; } Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL. Initially, all next pointers are set to NULL.

Solution

C++

Time O(n²)

Space O(1)

LeetCode

solution.cpp

/*
// Definition for a Node.
class Node {
public:
  int val;
  Node* left;
  Node* right;
  Node* next;

  Node() : val(0), left(NULL), right(NULL), next(NULL) {}

  Node(int _val) : val(_val), left(NULL), right(NULL), next(NULL) {}

  Node(int _val, Node* _left, Node* _right, Node* _next)
    : val(_val), left(_left), right(_right), next(_next) {}
};
*/

class Solution
{
public:
  Node *connect(Node *root)
  {
    if (!root)
      return nullptr;

    Node *leftmost = root;

    while (leftmost)
    {
      Node *curr = leftmost;
      Node *prev = nullptr;
      leftmost = nullptr;

      while (curr)
      {
        if (curr->left)
        {
          if (prev)
            prev->next = curr->left;
          else
            leftmost = curr->left;
          prev = curr->left;
        }
        if (curr->right)
        {
          if (prev)
            prev->next = curr->right;
          else
            leftmost = curr->right;
          prev = curr->right;
        }
        curr = curr->next;
      }
    }

    return root;
  }
};