[116]Populating Next Right Pointers in Each Node

最新推荐文章于 2024-08-25 16:11:27 发布

原创最新推荐文章于 2024-08-25 16:11:27 发布 · 176 阅读

0 ·

CC 4.0 BY-SA版权

leetcode 专栏收录该内容

140 篇文章

订阅专栏

本文详细介绍了如何使用递归和非递归方法解决二叉树节点连接问题，包括如何将每个节点的next指针指向其右侧相邻节点，并在完美二叉树上进行了实例演示。

【题目描述】

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,

After calling your function, the tree should look like:

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

【思路】

【代码】

递归：

/**
 * 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 dfs(TreeLinkNode *root,TreeLinkNode *child){
        if(root==NULL) return;
        else root->next=child;
        dfs(root->left,root->right);
        if(child==NULL){
            dfs(root->right,NULL);
        }
        else{
            dfs(root->right,child->left);
        }
    }
    void connect(TreeLinkNode *root) {
        dfs(root,NULL);
    }
    
};

感觉这个版本更好理解一点：

/**
 * 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) {
        if(root==NULL||(root->left==NULL&&root->right==NULL)) return;
        root->left->next=root->right;
        if(root->next!=NULL) root->right->next=root->next->left;
        connect(root->left);
        connect(root->right);
    }
};

非递归：

/**
 * 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) {
        if(root==NULL) return;
        TreeLinkNode *cur;
        while(root->left!=NULL){
            cur=root;
            while(cur){
                cur->left->next=cur->right;
                if(cur->next) cur->right->next=cur->next->left;
                cur=cur->next;
            }
            root=root->left;
        }
    }
};