删除带头结点的单链表最小值结点

删除带头结点的单链表最小值结点

王道19数据结构 P44
删除带头结点的单链表最小值结点（假设最小值结点唯一）

书上给的答案无法应对单链表为空的情况
因为指针为空时，无法访问其结构体成员

课本代码

LinkList DelMin(LinkList &L){
	LNode *pre = L, *p=pre->next; //L==NULL时此处报错
	LNode *minpre = pre, *min = p;
	while (p != NULL){
		if (p->data < min->data){
			min = p;
			minpre = pre;
		}
		pre = p;
		p = p->next;
	}
	minpre->next = min->next; //L->next==NULL时此处报错
	free(min);
	return L;
}

改进代码

加入空链表判断

LinkList DelMin(LinkList &L){
	if (L == NULL){
		return NULL;
	}
	if (L ->next == NULL){
		return NULL;
	}
	LNode *pre = L, *p=pre->next;
	LNode *minpre = pre, *min = p;
	while (p != NULL){
		if (p->data < min->data){
			min = p;
			minpre = pre;
		}
		pre = p;
		p = p->next;
	}
	minpre->next = min->next; 
	free(min);
	return L;
}

结构体定义

typedef char ElemType;
typedef struct LNode{
	ElemType data;
	struct LNode *next;
}LNode, *LinkList;

打印单链表

void printList(LinkList &L){
	LNode *p = L;
	if (p == NULL){
		printf("NULL1");
	}
	else if (p->next == NULL){
		printf("NULL2");
	}
	else{
		while (p != NULL){
			printf("%c ", p->data);
			p = p->next;
		}
	}
	printf("\n");
}

头文件及主函数

#include  
void main(){
	LNode *Head = (LNode*)malloc(sizeof(LNode)); //头结点
	LNode *A = (LNode*)malloc(sizeof(LNode));
	LNode *B = (LNode*)malloc(sizeof(LNode));
	LNode *C = (LNode*)malloc(sizeof(LNode));
	LNode *D = (LNode*)malloc(sizeof(LNode));
	LNode *E = (LNode*)malloc(sizeof(LNode));
	LNode *F = (LNode*)malloc(sizeof(LNode));
	LNode *G = (LNode*)malloc(sizeof(LNode));
	LNode *H = (LNode*)malloc(sizeof(LNode));
	LNode *I = (LNode*)malloc(sizeof(LNode));
	Head->data = '>';	Head->next = A;
	A->data = 'A';	A->next = B;
	B->data = 'B';	B->next = C;
	C->data = 'C';	C->next = D;
	D->data = 'D';	D->next = E;
	E->data = 'E';	E->next = F;
	F->data = 'F';	F->next = G;
	G->data = 'G';	G->next = H;
	H->data = 'H';	H->next = I;
	I->data = 'I';	I->next = NULL;
	LinkList L = (LinkList)malloc(sizeof(LNode));
	L = Head;
	//L->next = NULL;
	//L = NULL;
	DelMin(L);
	printList(L);
}