递归&&栈建立二叉树+先序，后序，中序，叶子数，节点数

#include<algorithm>
#include<set>
#include<vector>
#include<queue>
#include<cmath>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<set>
#include<vector>
#include<queue>
#include<cmath>
#include<cstdio>
#include<map>
#include<stack>
#include<string>
using namespace std;

#define sfi(i) scanf("%d",&i)
#define pri(i) printf("%d\n",i)
#define sff(i) scanf("%lf",&i)
#define ll long long
#define mem(x,y) memset(x,y,sizeof(x))
#define INF 0x3f3f3f3f
#define eps 1e-6
#define PI acos(-1)
#define lowbit(x) ((x)&(-x))
#define zero(x) (((x)>0?(x):-(x))<eps)
#define fl() printf("flag\n")
#define MOD(x) ((x%mod)+mod)%mod
#define FASTIO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
ll gcd(ll a,ll b){while(b^=a^=b^=a%=b);return a;}
const int maxn=2e5+9;
const int mod=1e9+7;

template <class T>
inline void sc(T &ret)
{
    char c;
    ret = 0;
    while ((c = getchar()) < '0' || c > '9');
    while (c >= '0' && c <= '9')
    {
        ret = ret * 10 + (c - '0'), c = getchar();
    }
}

char ch;
char s[maxn];

typedef struct BiNode
{
    char c;
    bool fl,fr;
    struct BiNode *lch,*rch;
}BiNode,*BiTree;

void CreateBiTree(BiTree &T)
{
    cin>>ch;
    if(ch=='#') T=NULL;
    else
    {
        T=new BiNode;
        T->c=ch;
        CreateBiTree(T->lch);
        CreateBiTree(T->rch);
    }
}

void CreateBiTree_Stack(BiTree &T,string s)
{
    int len=s.length();
    stack<BiTree>st;
    T=new BiNode;
    T->c=s[0];
    T->fl=false;
    T->fr=false;
    T->lch=NULL;
    T->rch=NULL;
    st.push(T);
    for(int i=1;i<len;i++)
    {
        //cout<<st.top()->c<<endl;
        if(s[i]!='#')
        {
            BiTree tmp=new BiNode;
            tmp->c=s[i];
            tmp->fl=false;
            tmp->fr=false;
            tmp->lch=NULL;
            tmp->rch=NULL;

            if(!st.top()->fl)
            {
                st.top()->lch=tmp;
                st.top()->fl=true;
            }
            else
            {
                st.top()->rch=tmp;
                st.top()->fr=true;
            }

            st.push(tmp);

        }
        else
        {
            if(!st.top()->fl)
            {
                st.top()->fl=true;
            }
            else
            {
                st.top()->fr=true;
            }
        }

        while(!st.empty()&&(st.top()->fl&&st.top()->fr))
        {
            //cout<<st.top()->c<<endl;;
            st.pop();
        }

    }
}

void MidSearch(BiTree &T)
{
    if(!T) return ;
    MidSearch(T->lch);
    cout<<T->c;
    MidSearch(T->rch);
}

void PreSearch(BiTree &T)
{
    if(!T) return ;
    cout<<T->c;
    PreSearch(T->lch);
    PreSearch(T->rch);
}

void PostSearch(BiTree &T)
{
    if(!T) return ;
    PostSearch(T->lch);
    PostSearch(T->rch);
    cout<<T->c;
}

int NodeCount(BiTree &T)
{
    if(!T) return 0;
    else return NodeCount(T->lch)+NodeCount(T->rch)+1;
}

int LeadCount(BiTree &T)
{
    if(!T) return 0;
    if(!T->lch&&!T->rch) return 1;
    else return LeadCount(T->lch)+LeadCount(T->rch);
}


int main()
{
    BiTree T;

    ////////////////////////////
    //栈建树
    int cnt=0;
    char c;
    while(c=getchar())
    {
        if(c=='\n') break;
        if(c==' ') continue;
        s[cnt++]=c;
    }
    //for(int i=0;i<cnt; i++) cout<<s[i];
    CreateBiTree_Stack(T,s);

    ////////////////////////////

    ////////////////////////////
    //递归建树
    //CreateBiTree(T);
    
    ////////////////////////////

    PreSearch(T);
    puts("");
    MidSearch(T);
    puts("");
    PostSearch(T);
    puts("");
    //cout<<NodeCount(T)<<endl;
    //cout<<LeadCount(T)<<endl;

    return 0;
}

/*
input:
A B # # C D # # #
output:
ABCD
BADC
BDCA

input:
A B C # # D E # G # # F # # #
output:
ABCDEGF
CBEGDFA
CGEFDBA

*/