Leetcode Populating Next Right Pointers in Each Node II

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

 題目看起來比較複雜，如果把它當做對二維陣列建立連結串列，此時就容易想了

主要難點就是有上一層如何去控制下一層，你可以根據連結串列的思路，用一個dummy結點，每次指向新的一行，然後根據按照連結串列遍歷思路，根據next結點去遍歷，一邊遍歷一邊新增下一層的結點。

class Solution {
public:
    void connect(TreeLinkNode *root) {
        if(root == NULL) return;
        root->next =NULL;
        TreeLinkNode *start = root, *nextStart = new TreeLinkNode(0),*p = nextStart;
        while(start){
            if(start->left) {p->next = start->left;p = p->next;}
            if(start->right){p->next = start->right;p = p->next;}
            if(start->next ==NULL ){
                p->next = NULL;
                start = nextStart->next;
                p = nextStart;
            }else start = start->next;
        }
    }
};