九度1078（二叉树已知先序和中序求后序）

题目链接：点击打开链接

解题思路：

很不错的一道题。用递归的方法求解。每次对两个序列进行递归，求得左子树的先序/中序，右子树的先序/中序。把树建好后调用递归输出后序即可

完整代码：

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

string fir , mid;

typedef struct Node
{
    char ch;
    struct Node *l;
    struct Node *r;
    Node()
    {
        l = NULL;
        r = NULL;
    };
}node;

void print(node *tree)
{
    if(tree == NULL)    return;
    print(tree->l);
    print(tree->r);
    cout << tree->ch;
}

void creat(node *&tree , string fir , string mid)
{
    if(fir.length() == 0)   return ;
    node *temp = new node();
    temp->ch = fir[0];
    tree = temp;
    int len = mid.find(fir[0]);

    string Lmid(mid , 0 , len);
    string Rmid(mid , len + 1 , mid.length() - len - 1);
    string Lfir(fir , 1 , len);
    string Rfir(fir , len + 1 , fir.length() - len - 1);

    creat(tree->l , Lfir , Lmid);
    creat(tree->r , Rfir , Rmid);
}

int main()
{
    #ifdef DoubleQ
    freopen("in.txt" , "r" , stdin);
    #endif // DoubleQ
    while(cin >> fir >> mid)
    {
        node *tree = NULL;
        creat(tree , fir , mid);
        print(tree);
        cout << endl;
    }
}