树结构复习笔记

本文最后更新于:2021年11月20日 下午

1. 重建二叉树

输入一棵二叉树前序遍历和中序遍历的结果,重建该二叉树。

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/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
unordered_map<int, int> pos;
vector<int> preorder, inorder;

TreeNode* build(int a,int b,int x,int y){
if(a>b) return NULL;
auto root=new TreeNode(preorder[a]);
int k=pos[root->val];
root->left=build(a+1, a+1+k-1-x ,x, k-1);
root->right=build(a+1+k-1-x+1, b, k+1, y);
return root;
}
TreeNode* buildTree(vector<int>& _preorder, vector<int>& _inorder) {
preorder=_preorder, inorder=_inorder;
int n=inorder.size();
for(int i=0;i<inorder.size();i++) pos[inorder[i]]=i;
return build(0, n-1, 0, n-1);
}
};

7078(线索二叉树,中序遍历)

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#include <iostream>
#include<cstdio>

using namespace std;

typedef struct BThrNode{
char data;
struct BThrNode *lchild, *rchild;
int ltag, rtag;
}BThrNode, *BThrTree;

BThrTree T,p;

void createBTree(BThrTree &T)
{
char ch;
cin>>ch;
if(ch=='@') T=NULL;
else
{
T=new BThrNode;
T->data=ch;
createBTree(T->lchild);
createBTree(T->rchild);
}
}
BThrTree pre=NULL;

void InThread(BThrTree p)
{
if(p!=NULL)
{
InThread(p->lchild);
if(p->lchild==NULL){p->ltag=1; p->lchild=pre;}
else p->ltag=0;
if(p->rchild==NULL){p->rtag=1; pre->rchild=p;}
else pre->rtag=0;
pre=p;
InThread(p->rchild);
}
}

void TraveBTree(BThrTree &T)
{
if(T)
{
TraveBTree(T->lchild);
cout<<T->data;
TraveBTree(T->rchild);
}
}
int main()
{
createBTree(T);
InThread(p);
TraveBTree(T);
return 0;
}

7079(中序遍历)

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#include <iostream>
#include<cstdio>

using namespace std;

typedef struct BTNode{
char data;
struct BTNode *lchild, *rchild;
//int ltag, rtag;
}BTNode, *BTree;

BTree T;

void createBTree(BTree &T)
{
char ch;
cin>>ch;
if(ch=='@') T=NULL;
else
{
T=new BTNode;
T->data=ch;
createBTree(T->lchild);
createBTree(T->rchild);
}
}

//void InThread(BThrTree p)
//{
// if(p!=NULL)
// {
// InThread(p->lchild);
// if(p->lchild==NULL){p->ltag=1; p->lchild=pre;}
// else p->ltag=0;
// if(p->rchild==NULL){p->rtag=1; pre->rchild=p;}
// else pre->rtag=0;
// pre=p;
// InThread(p->rchild);
// }
//}

void TraveBTree(BTree &T)
{
if(T)
{
TraveBTree(T->lchild);
cout<<T->data;
TraveBTree(T->rchild);
}
}
int main()
{
createBTree(T);
TraveBTree(T);
return 0;
}

7077(层次遍历)

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#include <iostream>
#include<cstdio>
#include <queue>

using namespace std;

const int MAX_SIZE=1010;

typedef struct BTNode{
char data;
struct BTNode *lchild, *rchild;
//int ltag, rtag;
}BTNode, *BTree;

typedef struct {
BTNode data[MAX_SIZE];
int front,rear;
}SQ;
BTree T;

void createBTree(BTree &T)
{
char ch;
cin>>ch;
if(ch=='@') T=NULL;
else
{
T=new BTNode;
T->data=ch;
createBTree(T->lchild);
createBTree(T->rchild);
}
}

//void InThread(BThrTree p)
//{
// if(p!=NULL)
// {
// InThread(p->lchild);
// if(p->lchild==NULL){p->ltag=1; p->lchild=pre;}
// else p->ltag=0;
// if(p->rchild==NULL){p->rtag=1; pre->rchild=p;}
// else pre->rtag=0;
// pre=p;
// InThread(p->rchild);
// }
//}

void TraveBTree(BTree &T)
{
BTree p;
queue<BTree> Q;
if(T)
{
Q.push(T);
while (!Q.empty())
{
p=Q.front();
cout<<p->data;
Q.pop();
if(p->lchild) Q.push(p->lchild);
if(p->rchild) Q.push(p->rchild);
}
}
}
int main()
{
createBTree(T);
TraveBTree(T);
return 0;
}

7080(父亲孩子表示法)

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#include<iostream>
#include<cstdio>

using namespace std;

typedef struct BTNode{
char data;
struct BTNode *lchild, *rchild;
}BTNode, *BTree;

BTree T;

void createBTree(BTree &T)
{
char ch;
cin>>ch;
if(ch=='@') T=NULL;
else
{
T=new BTNode;
T->data=ch;
createBTree(T->lchild);
createBTree(T->rchild);
}
}

int Trave(BTree T)
{
//int num=0;
if(!T) return 0;
else
{
if(T->lchild==NULL && T->rchild==NULL) return 1;
else return Trave(T->lchild)+ Trave(T->rchild);
}
return 0;
}

int Depth(BTree &T)
{
int m,n;
if(T==NULL) return 0;
else
{
m= Depth(T->lchild);
n= Depth(T->rchild);
if(m>n) return m+1;
else return n+1;
}
}

int CountLeaf(BTree &T)
{
int ans=0;
if(T==NULL) return 0;
if(T->lchild==NULL) return CountLeaf(T->rchild)+1;
else
return CountLeaf(T->lchild)+ CountLeaf(T->rchild);
}

int main()
{
createBTree(T);
//int ans= Depth(T);
cout<<CountLeaf(T)<<endl;
return 0;
}

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