数据结构之 二叉树---求二叉树后序遍历和层次遍历（先建树，再遍历）

#include <iostream>
#include <iomanip>
#include <string>
#include <string.h>
#include <stdio.h>
#include <algorithm>
#include <queue>
#include <vector>

using namespace std;

typedef struct node
{
    char a;
    struct node *ll;
    struct node *rr;
}Binode, *tree;

void build(int len, char *s1, char *s2, char *s) //先序中序 推 后序
{
    if(len<=0)
      return;
    int pos; //位置
    int i;

    for(i=0; i<len; i++)
    {
        if(s2[i]==s1[0])
        {
            pos=i;
            break;
        }
    }
    build(pos, s1+1, s2, s );
    build(len-pos-1, s1+pos+1, s2+pos+1, s+pos );
    s[len-1]=s1[0];
}  


//根据先序中序建树
struct node*creat(struct node *root, char *s, char *s1, int n)
{
    if(n<=0)
      return NULL;
    root=new node;
    root->a=s[0];

    int p=strchr(s1, s[0] )-s1;

    root->ll=creat( root->ll, s+1, s1, p );
    root->rr=creat( root->rr, s+p+1, s1+p+1, n-p-1 );

    return root;
}


//层次遍历 二叉树
void Level_Order(tree root)
{
    queue<tree>q;
    tree qq;

    if(root==NULL)
      return ;
    Binode *p=root;
    cout<<(p->a);

    if(p->ll)
      q.push( p->ll );
    if(p->rr)
      q.push( p->rr );

    while(!q.empty())
    {
        qq=q.front();
        q.pop();
        cout<<qq->a;
        if(qq->ll)
          q.push(qq->ll);
        if(qq->rr)
          q.push(qq->rr);
    }
    return;
}
int main()
{
    int t;
    cin>>t;
    char s1[100], s2[100];
    char s3[100];
    while(t--)
    {
        memset(s3, ‘\0‘, sizeof(s3));

        scanf("%s", s1); //中序
        scanf("%s", s2); //后序
        int len=strlen(s1);
        build(len, s1, s2, s3);
        printf("%s\n", s3); //输出后序遍历

        //计算层次遍历
        tree root, tt;
        root=creat(tt, s1, s2, len);
        
        Level_Order( root);
        cout<<endl;
    }
    return 0;
}

#include <iostream>
#include <iomanip>
#include <string>
#include <string.h>
#include <stdio.h>
#include <algorithm>
#include <queue>
#include <vector>

using namespace std;

typedef struct node
{
    char a;
    struct node *ll;
    struct node *rr;
}Binode, *tree;


//根据先序中序建树
struct node*creat(struct node *root, char *s, char *s1, int n)
{
    if(n<=0)
      return NULL;
    root=new node;
    root->a=s[0];

    int p=strchr(s1, s[0] )-s1;

    root->ll=creat( root->ll, s+1, s1, p );
    root->rr=creat( root->rr, s+p+1, s1+p+1, n-p-1 );

    return root;
}

void postorder(tree p)
{
    if(p)
    {
        postorder(p->ll);
        postorder(p->rr);
        printf("%c", p->a );
    }
}

//层次遍历 二叉树
void Level_Order(tree root)
{
    queue<tree>q;
    tree qq;

    if(root==NULL)
      return ;
    Binode *p=root;
    cout<<(p->a);

    if(p->ll)
      q.push( p->ll );
    if(p->rr)
      q.push( p->rr );

    while(!q.empty())
    {
        qq=q.front();
        q.pop();
        cout<<qq->a;
        if(qq->ll)
          q.push(qq->ll);
        if(qq->rr)
          q.push(qq->rr);
    }
    return;
}


int main()
{
    int t;
    cin>>t;
    char s1[100], s2[100];
    char s3[100];

    while(t--)
    {
        memset(s3, ‘\0‘, sizeof(s3));

        scanf("%s", s1); //中序
        scanf("%s", s2); //后序
        int len=strlen(s1);

        //计算层次遍历
        tree root, tt;
        root=creat(tt, s1, s2, len);
        postorder(root);
        cout<<endl;
        
        Level_Order( root);
        cout<<endl;
    }
    return 0;
}