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('\n');

        k = 1;

    }

    return 1;

}

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