表达式树

最新推荐文章于 2018-10-29 22:47:14 发布

原创最新推荐文章于 2018-10-29 22:47:14 发布 · 716 阅读

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CC 4.0 BY-SA版权

本文介绍了一种使用栈来构建表达式树的方法，并实现了前序、中序和后序遍历。通过分析给定的中缀表达式，创建相应的表达式树，最后展示了不同遍历方式下表达式的输出形式。

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/*
 *			Expression_Tree
 *			Date: 2013/3/19
 *								NolanJian
 */

#include <stdio.h>
#include <stdlib.h>
struct node;
struct stack;
typedef struct node Node;
typedef Node *NodePointer;
typedef struct stack Stack;
typedef Stack *StackPointer;

NodePointer Create(char *str);
NodePointer GetTop(StackPointer top);
void Push(StackPointer *top, NodePointer p);
void Pop(StackPointer *top);
void inorder(NodePointer p);
void preorder(NodePointer p);
void postorder(NodePointer p);

struct node {
	char ch;
	NodePointer LeftChild, RightChild;
};
struct stack {
	NodePointer p;
	StackPointer Next;
};

int main() {
	char *expression = "ab+cde+**";
	NodePointer root = Create(expression);
	preorder(root);
	printf("\n");
	inorder(root);
	printf("\n");
	postorder(root);
	printf("\n");
}

NodePointer Create(char *str) {
	NodePointer tp1, tp2, p;
	StackPointer top = NULL;
	while(*str) {
		if(*str >= 'a' && *str <= 'z') {
			p = (NodePointer)malloc(sizeof(Node));
			p->ch = *str;
			p->LeftChild = NULL;
			p->RightChild = NULL;
			Push(&top, p);
			str++;
			continue;
		}
		p = (NodePointer)malloc(sizeof(Node));
		tp1 = GetTop(top);
		Pop(&top);
		tp2 = GetTop(top);
		Pop(&top);
		p->ch = *str;
		p->LeftChild = tp2;
		p->RightChild = tp1;
		Push(&top, p);
		str++;
	}
	return top->p;
}

NodePointer GetTop(StackPointer top) {
	return top->p;
}

void Push(StackPointer *top, NodePointer p) {
	StackPointer tmp;
	if(*top == NULL){
		*top = (StackPointer)malloc(sizeof(Stack));
		(*top)->p = p;
		(*top)->Next = NULL;
	}
	tmp = (StackPointer)malloc(sizeof(Stack));
	tmp->p = p;
	tmp->Next = (*top);
	*top = tmp;
}

void Pop(StackPointer *top) {
	StackPointer p = *top;
	*top = (*top)->Next;
	free(p);
}

void inorder(NodePointer p) {
	if(p) {
		inorder(p->LeftChild);
		printf("%c", p->ch);
		inorder(p->RightChild);
	}
}

void preorder(NodePointer p) {
	if(p) {
		printf("%c", p->ch);
		preorder(p->LeftChild);
		preorder(p->RightChild);
	}
}

void postorder(NodePointer p) {
	if(p) {
		postorder(p->LeftChild);
		postorder(p->RightChild);
		printf("%c", p->ch);
	}
}