Populating Next Right Pointers in Each Node

描述

Given a binary tree

struct TreeLinkNode {
int val;
TreeLinkNode(int x) : val(x), left(NULL), right(NULL), next(NULL) {}
};


Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL.

Initially, all next pointers are set to NULL.

Note:

• You may only use constant extra space.
• You may assume that it is a perfect binary tree (ie, all leaves are at the same level, and every parent has two children).

For example,

         1
/  \
2    3
/ \  / \
4  5  6  7


After calling your function, the tree should look like:

         1 -> NULL
/  \
2 -> 3 -> NULL
/ \  / \
4->5->6->7 -> NULL


代码

// Populating Next Right Pointers in Each Node
// 时间复杂度O(n)，空间复杂度O(logn)
class Solution {
public:
connect(root, NULL);
}
private:
if (root == nullptr)
return;
else
root->next = sibling;

connect(root->left, root->right);
if (sibling)
connect(root->right, sibling->left);
else
connect(root->right, nullptr);
}
};