【二叉查找树】05根据升序的链表构造二叉查找树【Convert Sorted List to Binary Search Tree】
利用递归,构造二叉查找树,
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给一个升序的单向链表,把他转换成一个二叉查找树
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Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.
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test.cpp
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#include <iostream>
#include <cstdio> #include <cstdlib> #include <stack> #include <vector> #include "BinaryTree.h" #include "List.h" using namespace std; /** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ void findmid(ListNode *head, ListNode *end, ListNode *&mid) { if(head == NULL) { mid = NULL; return; } if(head->next == end) { mid = head; return; } /*pre就是传说中的快马*/ ListNode *pre = head; mid = head; while(pre->next != end) { pre = pre->next; if(pre->next != end) { pre = pre->next; } else { break; } mid = mid->next; } } TreeNode *tobst(ListNode *head, ListNode *tail) { if(head == tail) { return NULL; } if(head->next == tail) { int val = head->val; delete head; return new TreeNode(val); } ListNode *mid; findmid(head, tail, mid); TreeNode *tmp = new TreeNode(mid->val); tmp->left = tobst(head, mid); if(mid->next) { tmp->right = tobst(mid->next, tail); } delete mid; return tmp; } TreeNode *sortedListToBST(ListNode *head) { if(head == NULL) { return NULL; } return tobst(head, NULL); } vector<vector<int> > levelOrder(TreeNode *root) { vector<vector<int> > matrix; if(root == NULL) { return matrix; } vector<int> temp; temp.push_back(root->val); matrix.push_back(temp); vector<TreeNode *> path; path.push_back(root); int count = 1; while(!path.empty()) { TreeNode *tn = path.front(); if(tn->left) { path.push_back(tn->left); } if(tn->right) { path.push_back(tn->right); } path.erase(path.begin()); count--; if(count == 0) { vector<int> tmp; vector<TreeNode *>::iterator it = path.begin(); for(; it != path.end(); ++it) { tmp.push_back((*it)->val); } if(tmp.size() > 0) { matrix.push_back(tmp); } count = path.size(); } } return matrix; } // 树中结点含有分叉, // 4 // / \ // 2 6 // / \ / \ // 1 3 5 7 int main() { ListNode *pListNode1 = CreateListNode(1); ListNode *pListNode2 = CreateListNode(2); ListNode *pListNode3 = CreateListNode(3); ListNode *pListNode4 = CreateListNode(4); ListNode *pListNode5 = CreateListNode(5); ListNode *pListNode6 = CreateListNode(6); ListNode *pListNode7 = CreateListNode(7); ConnectListNodes(pListNode1, pListNode2); ConnectListNodes(pListNode2, pListNode3); ConnectListNodes(pListNode3, pListNode4); ConnectListNodes(pListNode4, pListNode5); ConnectListNodes(pListNode5, pListNode6); ConnectListNodes(pListNode6, pListNode7); TreeNode *root = sortedListToBST(pListNode1); vector<vector<int> > ans = levelOrder(root); for (int i = 0; i < ans.size(); ++i) { for (int j = 0; j < ans[i].size(); ++j) { cout << ans[i][j] << " "; } } cout << endl; DestroyTree(root); return 0; } |
输出结果:
4 2 6 1 3 5 7
List.h:
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#ifndef _LIST_H_
#define _LIST_H_ #include <cstdlib> struct ListNode { int val; ListNode *next; ListNode(int x) : val(x), next(NULL) {} }; ListNode *CreateListNode(int value); void ConnectListNodes(ListNode *pCurrent, ListNode *pNext); void PrintListNode(ListNode *pNode); void PrintList(ListNode *pHead); void DestroyList(ListNode *pHead); void AddToTail(ListNode **pHead, int value); void RemoveNode(ListNode **pHead, int value); #endif //_LIST_H_ |
List.cpp:
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#include "List.h"
#include <cstdio> #include <cstdlib> ListNode *CreateListNode(int value) { ListNode *pNode = new ListNode(0); pNode->val = value; pNode->next = NULL; return pNode; } void ConnectListNodes(ListNode *pCurrent, ListNode *pNext) { if(pCurrent == NULL) { printf("Error to connect two nodes.\n"); exit(1); } pCurrent->next = pNext; } void PrintListNode(ListNode *pNode) { if(pNode == NULL) { printf("The node is NULL\n"); } else { printf("The key in node is %d.\n", pNode->val); } } void PrintList(ListNode *pHead) { printf("PrintList starts.\n"); ListNode *pNode = pHead; while(pNode != NULL) { printf("%d\t", pNode->val); pNode = pNode->next; } printf("\nPrintList ends.\n"); } void DestroyList(ListNode *pHead) { ListNode *pNode = pHead; while(pNode != NULL) { pHead = pHead->next; delete pNode; pNode = pHead; } } void AddToTail(ListNode **pHead, int value) { ListNode *pNew = new ListNode(0); pNew->val = value; pNew->next = NULL; if(*pHead == NULL) { *pHead = pNew; } else { ListNode *pNode = *pHead; while(pNode->next != NULL) pNode = pNode->next; pNode->next = pNew; } } void RemoveNode(ListNode **pHead, int value) { if(pHead == NULL || *pHead == NULL) return; ListNode *pToBeDeleted = NULL; if((*pHead)->val == value) { pToBeDeleted = *pHead; *pHead = (*pHead)->next; } else { ListNode *pNode = *pHead; while(pNode->next != NULL && pNode->next->val != value) pNode = pNode->next; if(pNode->next != NULL && pNode->next->val == value) { pToBeDeleted = pNode->next; pNode->next = pNode->next->next; } } if(pToBeDeleted != NULL) { delete pToBeDeleted; pToBeDeleted = NULL; } } |
BinaryTree.h:
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#ifndef _BINARY_TREE_H_
#define _BINARY_TREE_H_ struct TreeNode { int val; TreeNode *left; TreeNode *right; TreeNode(int x) : val(x), left(NULL), right(NULL) {} }; TreeNode *CreateBinaryTreeNode(int value); void ConnectTreeNodes(TreeNode *pParent, TreeNode *pLeft, TreeNode *pRight); void PrintTreeNode(TreeNode *pNode); void PrintTree(TreeNode *pRoot); void DestroyTree(TreeNode *pRoot); #endif /*_BINARY_TREE_H_*/ |
BinaryTree.cpp:
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#include <iostream>
#include <cstdio> #include "BinaryTree.h" using namespace std; /** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ //创建结点 TreeNode *CreateBinaryTreeNode(int value) { TreeNode *pNode = new TreeNode(value); return pNode; } //连接结点 void ConnectTreeNodes(TreeNode *pParent, TreeNode *pLeft, TreeNode *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(TreeNode *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(TreeNode *pRoot) { PrintTreeNode(pRoot); if(pRoot != NULL) { if(pRoot->left != NULL) PrintTree(pRoot->left); if(pRoot->right != NULL) PrintTree(pRoot->right); } } void DestroyTree(TreeNode *pRoot) { if(pRoot != NULL) { TreeNode *pLeft = pRoot->left; TreeNode *pRight = pRoot->right; delete pRoot; pRoot = NULL; DestroyTree(pLeft); DestroyTree(pRight); } } |