Problem
You are given a perfect binary tree where all leaves are on the same level, and every parent has two children. The binary tree has the following definition:
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.
Follow up:
You may only use constant extra space.
Recursive approach is fine, you may assume implicit stack space does not count as extra space for this problem.
Solution
Constant Space
class Solution:
def connect(self, root: 'Node') -> 'Node':
node = root
while node:
next_level = node.left
while node and node.left:
node.left.next = node.right
node.right.next = node.next and node.next.left
node = node.next
node = next_level
return root