已知后序遍历和中序遍历求解前序遍历

/**
    author :  coder_zhang
    time   :  2014-6-14  
**/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define     MAX                        100
#define     ARRAY_SIZE(array, type)    (sizeof(array) / sizeof(type))

typedef struct node {
    int     value;
    struct node*  left;
    struct node*  right;
}  node;

void  pre_order(node* root) {
    node* stack[MAX];
    int   pos = -1;

    while (root != NULL || pos != -1) {
        if (root == NULL) {
            root = stack[pos--];
        }

        fprintf(stderr, "%c	", root->value);

        if (root->right != NULL) {
            stack[++pos] = root->right;
        }

        root = root->left;
    }

    fprintf(stderr, "
");
}

int  index_char(const char* str, char ch) {
    int  pos = 0;
    while (*str != '' && *str != ch) {
        ++pos;
        ++str;
    }
    return *str == '' ? -1 : pos;
}

void create_tree(node** root, const char* post_str, const char* in_str, int p_start, int p_end, int i_start, int i_end) {
    if (p_start <= p_end) {
        *root = (node*)malloc(sizeof(node));
        if (*root == NULL) {
            fprintf(stderr, "malloc memory failed!
");
            exit(1);
        }
        (*root)->value = post_str[p_end];
        (*root)->left = (*root)->right = NULL;
        int pos = index_char(in_str, post_str[p_end]);
        if (pos != -1) {
           int dis = pos - i_start;

           create_tree(&(*root)->left, post_str, in_str, p_start, p_start+dis-1, i_start, i_start+dis-1);
           create_tree(&(*root)->right, post_str, in_str, p_start+dis, p_end-1, pos+1, i_end);
        }
    }
}

int  main(void) {
    char  post_str[MAX];
    char  in_str[MAX];

    fprintf(stderr, "input post str:");
    fgets(post_str, MAX, stdin);
    post_str[strlen(post_str)-1] = '';

    fprintf(stderr, "input in str:");
    fgets(in_str, MAX, stdin);
    in_str[strlen(in_str)-1] = '';

    node*   root = NULL;

    create_tree(&root, post_str, in_str, 0, strlen(post_str)-1, 0, strlen(in_str)-1);

    pre_order(root);

    return  0;
}