• Question
• Solution

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[1024];
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: $O(1)$