蓝桥杯练习题—— 求先序排列

/*
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    Title: 蓝桥杯练习题—— 求先序排列
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    Date：2014/03/21
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    author：刘旭
************************************
*/
#include<iostream>
using namespace std;
string a, b;
typedef struct binary_tree
{
    char data;
    binary_tree *left, *right;
} bt;
bt* creat()
{
    bt *n = new bt;
    if(!n)
        return 0;
    n->left = n->right = NULL;
    return n;
}
int visit(bt *root)
{
    cout<<root->data;
    if(root->left)
        visit(root->left);
    if(root->right)
        visit(root->right);
    delete(root);
    root = NULL;
    return 0;
}
bt* build(int posa,int posb,int len)
{
    bt *root = NULL;
    if(len > 0)
    {
        root = creat();
        root->data = b[posb];
        int pos = a.find(root->data);
        int lenl =pos - posa;
        int lenr =len -1 - lenl;
        root->left = build(posa, posb-lenr-1, lenl);
        root->right = build(pos +1, posb-1, lenr);

    }
    return root;
}
int main()
{
    while(cin>>a>>b)
    {
        bt *root = build(0, b.length()-1, b.length());
        visit(root);
        cout<<endl;
    }
    return 0;
}