二叉树经典题解

例题：https://blog.youkuaiyun.com/qq_42866708/article/details/81409325
下面是全解；

#include <iostream>
#include <cstdio>
#include <queue>
using namespace std;

struct BiTNode{
    char data;
    struct BiTNode* lchild, * rchild;
};
BiTNode* T;
void CreateTree(BiTNode* &T){
    char ch;
    ch = getchar();
    if(ch != '#'){
        T = new BiTNode;
        T->data = ch;
        CreateTree(T->lchild);
        CreateTree(T->rchild);
    }else{
        T = NULL;
    }
}
void preorder(BiTNode* T){
    if(T){
        cout << T->data;
        preorder(T->lchild);
        preorder(T->rchild);
    }
}

void inorder(BiTNode* T){
    if(T){
        inorder(T->lchild);
        cout << T->data;
        inorder(T->rchild);
    }
}

void postorder(BiTNode* T){
    if(T){
        postorder(T->lchild);
        postorder(T->rchild);
        cout << T->data;
    }
}

void cengci(BiTNode* T){
    queue<BiTNode*> q;
    if(T){
        q.push(T);
        while(!q.empty()){
            T = q.front();
            q.pop();
            cout << T->data;
            if(T->lchild){
                q.push(T->lchild);
            }
            if(T->rchild){
                q.push(T->rchild);
            }
        }
    }
}
int main(){
    CreateTree(T);
    cout << "先序遍历：";
    preorder(T);
    cout << endl << "中序遍历：";
    inorder(T);  
    cout << endl << "后序遍历：";
    postorder(T);
    cout << endl << "层次遍历：";
    cengci(T); 
    return 0;
}

下面是另一种写法；

#include<stdio.h>
#include<stdlib.h>
#include<cstring>
#include<queue>
#include<iostream>
using namespace std;

typedef struct Node{
    struct Node* lchild;//左孩子 
    struct Node* rchild;//右孩子 
    char c;
}Node,*BiTree; 

BiTree creatTree(){//建树 
    char str;
    BiTree T;
    scanf("%c",&str);
    if(str=='#') 
        {
            T=NULL;
        }

    else{
        T = new Node;
        T->c = str;
        T->lchild = creatTree();
        T->rchild = creatTree();
        }
    return T; 
}
//先序遍历
void preOrder(BiTree T){
    if(T){
        printf("%c",T->c);
        preOrder(T->lchild);
        preOrder(T->rchild);
    }
} 
//中序遍历
void inOrder(BiTree T){
    if(T){
        inOrder(T->lchild);
        printf("%c",T->c);
        inOrder(T->rchild);
    }
} 
//后序
void postOrder(BiTree T){
    if(T){
        postOrder(T->lchild);
        postOrder(T->rchild);
        printf("%c",T->c);
    }
} 
 //层次
 void cengorder(BiTree T){
    BiTree P;
     queue <BiTree> Q;
    if(T){
        Q.push(T);
    }
    while(!Q.empty() ){
        P=Q.front() ;
        Q.pop() ;
        printf("%c",P->c );
        if(P->lchild !=NULL){
            Q.push(P->lchild ); 
        }   
        if(P->rchild !=NULL){
            Q.push(P->rchild );     
        }
    } 
  } 
int main(){
    BiTree T;
    T = creatTree();
    preOrder(T);
    inOrder(T);
    postOrder(T)；
    cengorder(T);
    return 0;
}