先序序列创建二叉树，输出先序序列、中序序列、后序序列并输出叶子结点数

#include<bits/stdc++.h>
using namespace std;
typedef struct node *tree;
struct node{
    tree left,right;
    char data;
};
int k;
tree build()
{
    char ch;
    cin>>ch;
    tree t=(tree)new(tree);
    if(ch=='#') t=NULL;
    else
    {
        t->data=ch;
        t->left=build();
        t->right=build();
        if(t->left==NULL&&t->right==NULL) k++;
    }
    return t;
}
void xian(tree t)
{
    if(t)
    {
        cout<<t->data;
        xian(t->left);
        xian(t->right);
    }
}
void zhong(tree t)
{
    if(t)
    {
        zhong(t->left);
        cout<<t->data;
        zhong(t->right);
    }
}
void hou(tree t)
{
    if(t)
    {
        hou(t->left);
        hou(t->right);
        cout<<t->data;
    }
}
int main()
{
    tree t=build();
    if(t)
    {
        xian(t);
        cout<<endl;
        zhong(t);
        cout<<endl;
        hou(t);
        cout<<endl;
    }
    cout<<k;
    return 0;
}