已知先序和中序，求后序

思路：

由先序找到根节点，即先序的第一个元素，

然后从中序中找到它的位置，以确定左右孩子，即它的左右两边的元素

依次递归

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define status int
#define OK 1
#define ERROR 0
#define OVERFLOW -1 
int k = 1;
typedef struct Node{

    char data;
    Node *left; 
    Node *right;

}*Tree;
status Recover(Tree &T, char Pr[], char In[], int s, int e)
{
    if(s > e) return ERROR;
    if(!T)
    {
        T = (Tree)malloc(sizeof(Node));
        T->data = Pr[k++];
        T->left = T->right = NULL;
    }
    int i;
    for(i = s; i <= e; i++)
        if(Pr[k-1] == In[i])
            break;
    Recover(T->left, Pr, In, s, i-1);
    Recover(T->right, Pr, In, i+1, e);
    return OK;
}
status Ba(Tree T)
{
    if(!T) return ERROR;
    Ba(T->left);
    Ba(T->right);
    printf("%c", T->data);
    return OK;
}
int main()
{
    char Pr[27], In[27];
    int m;
    while(scanf("%s %s", Pr+1, In+1) != EOF)
    {
        Tree T = NULL;
        m = strlen(Pr+1);
        Recover(T, Pr, In, 1, m);
        Ba(T);
        putchar('
');
        k = 1;
    }
    return 1;
}