【遍历二叉树】12往二叉树中添加层次链表的信息【Populating Next Right Pointers in Each Node II】

本质上是二叉树的层次遍历，遍历层次的过程当中把next指针加上去。

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和问题"Populating Next Right Pointers in Each Node"类似。

如果给定的树是任意的二叉树，你先前的方法还能工作吗？

笔记：

• 你只能用常量的辅助空间。

例如给定的是羡慕的二叉树，

         1
       /  \
      2    3
     / \    \
    4   5    7

当调用完你的函数后，这个树应该看起来想这样子：

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

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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

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test.cpp：

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#include <iostream> #include <cstdio> #include <stack> #include <vector> #include "BinaryTreeWithNext.h" using namespace std; /**  * 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) {}  * };  */ void connect(TreeLinkNode *root) {     if(root == NULL)     {         return ;     }     vector<TreeLinkNode *> vec;     vec.push_back(root);     int count = 1;     while(!vec.empty())     {         if(count > 1)         {             vec[0]->next = vec[1];         }         else         {             vec[0]->next = NULL;         }         if(vec[0]->left != NULL)         {             vec.push_back(vec[0]->left);         }         if(vec[0]->right != NULL)         {             vec.push_back(vec[0]->right);         }         vec.erase(vec.begin());         count--; if(count == 0)         {             count = vec.size();         }     } } // 树中结点含有分叉， //                  1 //              /       \ //             2         3 //           /   \         \ //          4     5         7 int main() {     TreeLinkNode *pNodeA1 = CreateBinaryTreeNode(1);     TreeLinkNode *pNodeA2 = CreateBinaryTreeNode(2);     TreeLinkNode *pNodeA3 = CreateBinaryTreeNode(3);     TreeLinkNode *pNodeA4 = CreateBinaryTreeNode(4);     TreeLinkNode *pNodeA5 = CreateBinaryTreeNode(5);     TreeLinkNode *pNodeA6 = CreateBinaryTreeNode(7); ConnectTreeNodes(pNodeA1, pNodeA2, pNodeA3);     ConnectTreeNodes(pNodeA2, pNodeA4, pNodeA5);     ConnectTreeNodes(pNodeA3, NULL, pNodeA6); connect(pNodeA1); TreeLinkNode *trav = pNodeA1;     TreeLinkNode *tmp;     while (trav != NULL)     {         tmp = trav;         while(tmp)         {             cout << tmp->val << " ";             tmp = tmp->next;         }         cout << endl;         trav = trav->left;     }     cout << endl; DestroyTree(pNodeA1);     return 0; }

结果输出：

1

2 3

4 5 7

BinaryTreeWithNext.h：

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#ifndef _BINARY_TREE_WITH_NEXT_H_ #define _BINARY_TREE_WITH_NEXT_H_ struct TreeLinkNode {     int val;     TreeLinkNode *left;     TreeLinkNode *right;     TreeLinkNode *next;     TreeLinkNode(int x) : val(x), left(NULL), right(NULL), next(NULL) {} }; TreeLinkNode *CreateBinaryTreeNode(int value); void ConnectTreeNodes(TreeLinkNode *pParent,                       TreeLinkNode *pLeft, TreeLinkNode *pRight); void PrintTreeNode(TreeLinkNode *pNode); void PrintTree(TreeLinkNode *pRoot); void DestroyTree(TreeLinkNode *pRoot); #endif /*_BINARY_TREE_WITH_NEXT_H_*/

BinaryTreeWithNext.cpp：

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#include <iostream> #include <cstdio> #include "BinaryTreeWithNext.h" using namespace std; /**  * 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) {}  * };  */ //创建结点 TreeLinkNode *CreateBinaryTreeNode(int value) {     TreeLinkNode *pNode = new TreeLinkNode(value); return pNode; } //连接结点 void ConnectTreeNodes(TreeLinkNode *pParent, TreeLinkNode *pLeft, TreeLinkNode *pRight) {     if(pParent != NULL)     {         pParent->left = pLeft;         pParent->right = pRight;     } } //打印节点内容以及左右子结点内容 void PrintTreeNode(TreeLinkNode *pNode) {     if(pNode != NULL)     {         printf("value of this node is: %d\n", pNode->val); if(pNode->left != NULL)             printf("value of its left child is: %d.\n", pNode->left->val);         else             printf("left child is null.\n"); if(pNode->right != NULL)             printf("value of its right child is: %d.\n", pNode->right->val);         else             printf("right child is null.\n");     }     else     {         printf("this node is null.\n");     } printf("\n"); } //前序遍历递归方法打印结点内容 void PrintTree(TreeLinkNode *pRoot) {     PrintTreeNode(pRoot); if(pRoot != NULL)     {         if(pRoot->left != NULL)             PrintTree(pRoot->left); if(pRoot->right != NULL)             PrintTree(pRoot->right);     } } void DestroyTree(TreeLinkNode *pRoot) {     if(pRoot != NULL)     {         TreeLinkNode *pLeft = pRoot->left;         TreeLinkNode *pRight = pRoot->right; delete pRoot;         pRoot = NULL; DestroyTree(pLeft);         DestroyTree(pRight);     } }