二叉树的非递归实现

二叉树的概念就不多讲，直接上代码：

#include <stdio.h>#include <stdlib.h>#define STACK_INIT_SIZE10#define INCREASE_SIZE10typedef struct Node{char data;struct Node *left;struct Node *right;int lflag;int rflag;}Node, *BTree;typedef struct {Node **base;int top;int curlen;}NodeStack;void init_stack(NodeStack *s){s->base = (Node**)malloc(STACK_INIT_SIZE*sizeof(Node*));if (!s->base){printf("Init stack error\n");return ;}s->top = 0;s->curlen = STACK_INIT_SIZE;}void free_stack(NodeStack *s){if (s->base){free(s->base);s->base = NULL;s->top = s->curlen = 0;}}int is_stack_empty(NodeStack s){return s.top <= 0;}int is_stack_full(NodeStack s){return s.top >= s.curlen;}void push_node(NodeStack *s, Node *pnode){if (is_stack_full(*s)){Node **tmp;tmp = (Node**)realloc(s->base, (s->curlen+INCREASE_SIZE)*sizeof(Node*));if (!tmp){printf("push error\n");free_stack(s);return ;}s->curlen += INCREASE_SIZE;}(s->base)[s->top] = pnode;(s->top)++;}Node* pop_node(NodeStack *s){if (is_stack_empty(*s)){return NULL;}(s->top)--;return (s->base)[s->top];}

//先序创建二叉树BTree dlr_create_tree(){char data;printf("Enter the root node:\n");scanf("%c", &data);getchar();if (data == '#'){return NULL;}Node* rootnode;rootnode = (Node*)malloc(sizeof(Node));if (!rootnode){printf("dlr_create_tree error\n");return NULL;}rootnode->data = data;rootnode->left = NULL;rootnode->lflag = 0;rootnode->right = NULL;rootnode->rflag = 0;Node *curnode;curnode = rootnode;NodeStack s;init_stack(&s);while (1){if (!curnode->lflag){curnode->lflag = 1;printf("Enter the left node of %c:\n",curnode->data);char c;scanf("%c", &c);getchar();if (c != '#'){Node *curleft;curleft = (Node*)malloc(sizeof(Node));if (curleft){curleft->data = c;curleft->left = NULL;curleft->lflag = 0;curleft->right = NULL;curleft->rflag = 0;curnode->left = curleft;push_node(&s, curnode);curnode = curleft;continue;}}}if (!curnode->rflag){curnode->rflag = 1;printf("Enter the right node of %c:\n", curnode->data);char c;scanf("%c", &c);getchar();if (c != '#'){Node *curright;curright = (Node*)malloc(sizeof(Node));if (curright){curright->data = c;curright->left = NULL;curright->lflag = 0;curright->right = NULL;curright->rflag = 0;curnode->right = curright;curnode = curright;}}else {if (is_stack_empty(s)){break;}else{curnode = pop_node(&s);}}}}free_stack(&s);return rootnode;}

//先序遍历二叉树void dlr_vist_tree(BTree t){if (!t){return;}NodeStack s;init_stack(&s);Node *curnode;curnode = t;while (1){printf("%3c", curnode->data);if (curnode->left){push_node(&s, curnode);curnode = curnode->left;continue;}if (curnode->right){curnode = curnode->right;}else{Node *tmp = NULL;while (!is_stack_empty(s)){tmp = pop_node(&s);if (tmp->right){curnode = tmp->right;break;}}if (is_stack_empty(s) && (!tmp || !tmp->right)){break;}}}free_stack(&s);printf("\n");}//中序遍历二叉树void ldr_vist_tree(BTree t){if (!t){return;}NodeStack s;Node *curnode;curnode = t;init_stack(&s);while (1){if (curnode->left){push_node(&s, curnode);curnode = curnode->left;continue;}printf("%3c", curnode->data);if (curnode->right){curnode = curnode->right;}else{Node *tmp;tmp = NULL;while (!is_stack_empty(s)){tmp = pop_node(&s);printf("%3c", tmp->data);if (tmp->right){curnode = tmp->right;break;}}if (is_stack_empty(s) && (!tmp || !(tmp->right))){break;}}}printf("\n");free_stack(&s);}

//释放二叉树void free_tree(BTree t){if (!t){return;}Node *curnode;curnode = t;NodeStack s;init_stack(&s);while (1){if (curnode->left || curnode->right){push_node(&s, curnode);if (curnode->left){curnode = curnode->left;continue;}if (curnode->right){curnode = curnode->right;}}else{if (is_stack_empty(s)){printf("free node %c\n", curnode->data);free(curnode);break;}Node *tmp;tmp = pop_node(&s);if (curnode == tmp->left){tmp->left = NULL;}if (curnode == tmp->right){tmp->right = NULL;}printf("free node %c\n", curnode->data);free(curnode);curnode = tmp;}}free_stack(&s);}//后序遍历二叉树void lrd_vist_tree(BTree t){if (!t){return;}Node *curnode;NodeStack s;curnode = t;init_stack(&s);while (1){if (curnode->lflag || curnode->rflag){if (curnode->lflag && curnode->left){push_node(&s, curnode);curnode = curnode->left;continue;}if (curnode->rflag && curnode->right){push_node(&s, curnode);curnode = curnode->right;continue;}else{curnode->lflag = curnode->rflag = 0;}}else{printf("%3c", curnode->data);if (is_stack_empty(s)){break;}Node *tmp = NULL;while (!is_stack_empty(s)){tmp = pop_node(&s);if (curnode == tmp->left){tmp->lflag = 0;if (tmp->right){push_node(&s, tmp);curnode = tmp->right;}else{tmp->rflag = 0;curnode = tmp;}break;}else if(curnode == tmp->right){tmp->rflag = 0;curnode = tmp;break;}}}}free_stack(&s);printf("\n");}int main(){BTree bt;bt = dlr_create_tree();printf("DLR visit:\n");dlr_vist_tree(bt);printf("LDR visit:\n");ldr_vist_tree(bt);printf("LRD visti:\n");lrd_vist_tree(bt);free_tree(bt);return 0;}