Populating Next Right Pointers in Each Node
Total Accepted: 81093 Total Submissions: 222510 Difficulty: Medium
Given a binary tree
struct TreeLinkNode {
TreeLinkNode *left;
TreeLinkNode *right;
TreeLinkNode *next;
}
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,
Given the following perfect binary tree,
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
思路
使用了queue就很简单但是不是constant space
public class Solution {
public void connect(TreeLinkNode root) {
if (root == null) {
return;
}
TreeLinkNode cur = root;
Queue<TreeLinkNode> queue = new LinkedList<TreeLinkNode>();
queue.offer(cur);
while (!queue.isEmpty()) {
int size = queue.size();
TreeLinkNode pre = null;
for (int i = 0; i < size; i++) {
cur = queue.poll();
if (pre != null) {
pre.next = cur;
}
pre = cur;
if (cur.left != null) {
queue.offer(cur.left);
}
if (cur.right != null) {
queue.offer(cur.right);
}
}
}
}
}
O(1) Space
public class Solution {
public void connect(TreeLinkNode root) {
if (root == null) {
return;
}
if (root.left != null) {
root.left.next = root.right;
}
if (root.right != null && root.next != null) {
root.right.next = root.next.left;
}
connect(root.left);
connect(root.right);
}
}