Data structure Wangdao postgraduate study book linked list practice questions --- an efficient algorithm to delete a minimum node

Topic description:

Try to write an efficient algorithm for deleting a minimum node in a singly linked list L with a head node (assuming that the minimum node is unique)

The idea of ​​​​the answer is very clear, but I didn't expect it at first. The idea I thought of is as follows (more straight, not as advanced as the answer):

Ideas:

1. The first thing to remember is that if we want to delete or insert an element in the singly linked list , we must write it down 被删除的元素的前驱结点, because the successor node can be obtained from the predecessor node->next->next no matter how bad it is. So the precursor node is a must!
2. In this question, we need to constantly compare the data value of each node, and then record the predecessor of the current smallest node.
3. So, my idea is to constantly compare p->next, then the predecessor node is p.
4. And a q pointer needs to be used to track p (pointing to p), because p->next needs to be constantly compared, so p needs to move backward, and every time it is currently 最小的那个节点的前驱recorded by the q pointer

Specific code (runnable):

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

typedef struct LNode{
    
    
	int data;
	struct LNode *next;
}LNode,*LinkList;

LinkList Init(LinkList L){
    
    
	int x;
	L = (LinkList)malloc(sizeof(LNode));
	LinkList r,s;
	r = L;
	printf("请输入元素:\n");
	scanf("%d",&x);
	while(x!= 999){
    
    
		s = (LNode*)malloc(sizeof(LNode));
		s->data = x;
		r->next = s;
		r = s;
		printf("请输入元素:\n");
		scanf("%d",&x);
	}
	r->next = NULL;
	return L;
} 

void print(LinkList L){
    
    
	LinkList p;
	p = L->next;
	while(p!= NULL) {
    
    
		printf("%5d",p->data);
		p = p->next;
	} 
	printf("\n"); 
}

void Del_min(LinkList L){
    
    
	LinkList p,q,r;
	int min;
	p = L;
	min = p->next->data;
	while(p->next != NULL){
    
    
		if(p->next->data <= min){
    
    
			min = p->next->data;
			q = p;
		}
			p = p->next;
	}
	r = q->next;
	q->next = r->next;
	free(r);
	print(L);
}



int main(){
    
    
	LinkList L,L1;
	L1 = Init(L);
	printf("打印初始链表:\n");
	print(L1);
	printf("打印删除最小值之后的链表:\n");
	Del_min(L1);
	return 0;
}

Write the answer:

void Del_min(LinkList L){
	LinkList p,q,r;
	int min;
	p = L;
	min = p->next->data;
	while(p->next != NULL){
		if(p->next->data <= min){
			min = p->next->data;
			q = p;
		}
			p = p->next;
	}
	r = q->next;
	q->next = r->next;
	free(r);
}