LeetCode(116) Populating Next Right Pointers in Each Node

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/** * 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 == NULL)            return;        if(root->left == NULL)            return;        if(root->next == NULL) {            root->left->next = root->right;            root->right->next = NULL;        }        if(root->next != NULL) {            root->left->next = root->right;            root->right->next = root->next->left;        }        connect(root->left);        connect(root->right);    }};