LeetCode 116: Populating Next Right Pointers in Each Node Solution

Master LeetCode problem 116 (Populating Next Right Pointers in Each Node), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

116. Populating Next Right Pointers in Each Node

Medium

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

Problem Explanation

Explanation

To solve this problem, we can utilize a level order traversal approach with constant extra space. We can use the next pointers already present in the nodes to connect the nodes at the same level.

We start from the root and keep moving level by level.
For each level, we iterate through the nodes at that level and connect their children using the next pointers.
The next pointers at each level are already set correctly for the previous level, so we can utilize this to connect the nodes at the current level.
We continue this process until we reach the last level of the tree.

Time Complexity: O(N) where N is the number of nodes in the binary tree.

Space Complexity: O(1) since we are using constant extra space.

Solution Code

class Solution {
    public Node connect(Node root) {
        if (root == null) {
            return null;
        }
        
        Node levelStart = root;
        
        while (levelStart.left != null) {
            Node curr = levelStart;
            
            while (curr != null) {
                curr.left.next = curr.right;
                if (curr.next != null) {
                    curr.right.next = curr.next.left;
                }
                
                curr = curr.next;
            }
            
            levelStart = levelStart.left;
        }
        
        return root;
    }
}

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