根据前序和中序遍历结果构造二叉树

//binarytree.h
#ifndef BINARYTREE_H
#define BINARYTREE_H
typedef struct node *link;
struct node {
	unsigned char item;
	link l, r;
};

link tree_init(unsigned char VLR[], unsigned char LVR[], int n);
void pre_order(link t, void (*visit)(link));
void in_order(link t, void (*visit)(link));
void post_order(link t, void (*visit)(link));
int count(link t);
int depth(link t);
void destroy(link t);
#endif

###############################################################

//binarytree.c
#include <stdlib.h>
#include "binarytree.h"

static link make_node(unsigned char item){
	link p = malloc(sizeof *p);
	p->item = item;
	p->l = p->r = NULL;
	return p;
}

static void free_node(link p){
	free(p);
}

link tree_init(unsigned char VLR[], unsigned char LVR[], int n){
	// 子树的先序、中序、子树的包括元素的个数
	link t;
	int k;
	if (n <= 0)
		return NULL;
	for (k = 0; VLR[0] != LVR[k]; k++); //在中序中寻找根节点
	t = make_node(VLR[0]);
	t->l = tree_init(VLR+1, LVR, k); //构建左子树
	t->r = tree_init(VLR+1+k, LVR+1+k, n-k-1); //构建右子树
	return t;
}

void pre_order(link t, void (*visit)(link)){
	if (!t)
		return;
	visit(t);
	pre_order(t->l, visit);
	pre_order(t->r, visit);
}

void in_order(link t, void (*visit)(link)){
	if (!t)
		return;
	in_order(t->l, visit);
	visit(t);
	in_order(t->r, visit);
}

void post_order(link t, void (*visit)(link)){
	if (!t)
		return;
	post_order(t->l, visit);
	post_order(t->r, visit);
	visit(t);
}

int count(link t){
	if (!t)
	return 0;
	return 1 + count(t->l) + count(t->r);
}

int depth(link t){
	int dl, dr;
	if (!t)
		return 0;
	dl = depth(t->l);
	dr = depth(t->r);
	return 1 + (dl > dr ? dl : dr);
}

void destroy(link t){
	post_order(t, free_node);
}

###############################################################

//main.c
#include <stdio.h>
#include "binarytree.h"

void print_item(link p){
	printf("%d", p->item);
}

int main(){
	unsigned char pre_seq[] = { 4, 2, 1, 3, 6, 5, 7 };
	unsigned char in_seq[] = { 1, 2, 3, 4, 5, 6, 7 };
	link root = tree_init(pre_seq, in_seq, 7);
	pre_order(root, print_item);
	putchar('\n');
	in_order(root, print_item);
	putchar('\n');
	post_order(root, print_item);
	putchar('\n');
	printf("count=%d depth=%d\n", count(root), depth(root));
	destroy(root);
	return 0;
}