[LeetCode] Populating Next Right Pointers in Each Node II

Populating Next Right Pointers in Each Node IIOct 28 '12423 / 1042

Follow up for problem "Populating Next Right Pointers in Each Node".

What if the given tree could be any binary tree? Would your previous solution still work?

Note:

• You may only use constant extra space.

 

For example,
Given the following binary tree,

         1
       /  \
      2    3
     / \    \
    4   5    7

 

After calling your function, the tree should look like:

         1 -> NULL
       /  \
      2 -> 3 -> NULL
     / \    \
    4-> 5 -> 7 -> NULL

 

 

 

 

 

/**
 * 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;
        root->next = NULL;
        TreeLinkNode* par = root;
        int left = 0;
        TreeLinkNode* cur = get_next_child(par, left);
        while (cur !=NULL) {
            TreeLinkNode* head = cur;
            while (cur != NULL) {
                cur->next = get_next_child(par, left);
                cur = cur->next;
            }
            par = head;left = 0;
            cur = get_next_child(par, left);
        }
    }
    TreeLinkNode* get_next_child(TreeLinkNode* & par, int& left) {
        if (left == 2) par = par->next;
        if (left == 1)
            if (par->right != NULL) {left = 2; return par->right; }
            else par = par->next;
        while (par != NULL) {
            if (par->left != NULL) { left=1; return par->left;}
            if (par->right != NULL){ left=2; return par->right;}
            par = par->next;
        }
        return NULL;
    }
    
};