populating-next-right-pointers-in-each-node.cpp

/**
 * Definition for binary tree with next pointer.
 * struct TreeLinkNode {
 *  int val;
 *  TreeLinkNode *left, *right, *next;
 *  TreeLinkNode(int x) : val(x), left(NULL), right(NULL), next(NULL) {}
 * };
 */
class Solution {
public:
    void connect(TreeLinkNode *root) {
        if(root == nullptr) 
            return;  
        if(root->left)
            root->left->next = root->right;  
        if(root->right)  
            root->right->next = root->next ? root->next->left : nullptr;
        connect(root->left); 
        connect(root->right);
    }
};