## Populating Next Right Pointers in Each Node II

07/11/2016 Tree Depth First Search

## Question

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


## Solution

Result: Accepted Time: 8 ms

Here should be some explanations.

struct TreeLinkNode * stck;
void dfs(struct TreeLinkNode * root ,int depth)
{
if(root == NULL) return ;
root->next = NULL;
if(stck[depth])
stck[depth]->next = root;
stck[depth] = root;
dfs(root->left,depth + 1);
dfs(root->right,depth + 1);
}
void connect(struct TreeLinkNode *root) {
memset(stck,0,sizeof(stck));
dfs(root,0);
}


Complexity Analytics

• Time Complexity: $O(n)$
• Space Complexity: $O(1)$