算法基础题——链表

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct ListNode{
	char value;
	struct ListNode * next;
}ListNode;


//单链表倒置——头插法
ListNode * listReverse(ListNode * head){
	if(NULL == head){
		return NULL;
	}
	if(NULL == head->next){
		return head;
	}

	ListNode * p = head->next;
	head->next = NULL;
	ListNode * tmp;
	while(p){
		tmp = p->next;
		p->next = head->next;
		head->next = p;
		p = tmp;
	}
	
	return head;
}
//创建单链表
ListNode * makeList(char * src, ListNode *head){
	if(NULL == src){
		return NULL;
	}
	//创建头结点
	head = (ListNode *) malloc(sizeof(ListNode));
	head->next = NULL;
	ListNode *p = head;

	while(*src != '\0'){
		ListNode * node = (ListNode *) malloc(sizeof(ListNode));
		if(NULL == node){
			return NULL;
		}
		p->next = node;
		p = p->next;
		p->value = *src;
		p->next = NULL;
		src++;
	}

	return head;
}

int main(){
	char *src = "abcde";
	ListNode * head, *tmp;
	head = makeList(src, head);
	tmp = head;
	do{
		tmp = tmp->next;
		printf("######%c\n", tmp->value);
	}while(tmp->next);
	
	head = listReverse(head);
	tmp = head;
	do{
		tmp = tmp->next;
		printf("******%c\n", tmp->value);
	}while(tmp->next);
	
	free(head);//释放malloc分配的堆空间
	head = NULL;//释放后，将指针置为NULL，防止后面的程序误用
}