Populating Next Right Pointers in Each Node,Populating Next Right Pointers in Each Node II

Populating Next Right Pointers in Each Node

Total Accepted: 72323 Total Submissions: 199207 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

(H) Populating Next Right Pointers in Each Node II (M) Binary Tree Right Side View
深度优先遍历，这题跟判断是否是镜像二叉树的思路是一样的。

/**
* 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* root1,TreeLinkNode* root2){
if(!root1) return;

root1->next = root2;

dfs(root1->left,root1->right);

if(!root2) return;

dfs(root1->right,root2->left);
dfs(root2->left,root2->right);
}
void connect(TreeLinkNode *root) {
if(!root) return ;
dfs(root->left,root->right);
}
};

Next challenges: (H) Populating Next Right Pointers in Each Node II

Populating Next Right Pointers in Each Node II

Total Accepted: 51329 Total Submissions: 158800 Difficulty: Hard

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

广度优先遍历

/**
* 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) return ;

TreeLinkNode* head = NULL;
TreeLinkNode* tail = NULL;
TreeLinkNode* cur  = root;

while(cur){
if(cur->left){
if(tail){
tail->next = cur->left;
tail = cur->left;
}else{
tail = cur->left;
head = cur->left;
}
}
if(cur->right){
if(tail){
tail->next = cur->right;
tail = cur->right;
}else{
tail = cur->right;
head = cur->right;
}
}
cur = cur->next;
if(!cur){
cur = head;
tail = NULL;
head = NULL;
}
}
}
};