116. Populating Next Right Pointers in Each Node
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116. Populating Next Right Pointers in Each Node
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 toNULL
.
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
题目大意
给定一个二叉树是一个完美二叉树(每个父节点都有两个子节点)。
将其每层上的节点从左到右使用next指针连接起来,如果没有右边的节点,则用NULL代替。
解题思路
- 使用BFS遍历整棵树。
- 这个方法的关键点在于,将每一层结尾的
NULL
push入队列(以读到上一层结尾的NULL
为标志 push)。 - 如果出现连续的
NULL
说明遍历结束。
算法复杂度
代码实现
/** * Definition for binary tree with next pointer. * struct TreeLinkNode { * int val; * TreeLinkNode *left, *right, *next; * TreeLinkNode(int x) : val(x), left(NULL), right(NULL), next(NULL) {} * }; */class Solution {public: void connect(TreeLinkNode *root) { queue<TreeLinkNode *> que; TreeLinkNode *cache = nullptr; TreeLinkNode *top = nullptr; que.push(root); que.push(nullptr); // key // bfs while (!que.empty()) { top = que.front(); que.pop(); if (top != nullptr) { top->next = que.front(); que.push(top->left); que.push(top->right); } else { // 如果出现连续的nullptr, 则说明bfs已经结束 if (que.front() == nullptr) break; que.push(nullptr); // 层结束标志 } } }};
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- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
- Populating Next Right Pointers in Each Node
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