根据前序和中序遍历结果构造二叉树

/* binarytree.h */#ifndef BINARYTREE_H#define BINARYTREE_Htypedef struct node *link;struct node {unsigned char item;link l, r;};link 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);}/* * VLR 前序遍历 * LVR 中序遍历 * n   节点个数 */link init(unsigned char VLR[], unsigned char LVR[], int n){link t;int k;if (n <= 0)return NULL;        /*         * 前序遍历中的第一个元素就是根节点所以依据这个可以求出         * 在根节点在中序的下标（位置）          */for (k = 0; VLR[0] != LVR[k]; k++);        /* 循环结束后k就是根节点的在中序遍历中的位置 */        /* 跟左边的就是左子树（k个），右边的就是右字树（n-k-1个）*/t = make_node(VLR[0]);t->l = init(VLR+1, LVR, k);t->r = init(VLR+1+k, LVR+1+k, n-k-1);        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 = 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;}

 

前序和中序遍历的结果合在一起可以唯一确定二叉树的形态，

也就是说根据遍历结果可以构造出二叉树.