牛客网-刷题-BM1 反转链表

#include 


struct ListNode {
int val;
struct ListNode *next;
};

struct ListNode* ReverseList(struct ListNode* pHead ) {
    if (pHead == NULL) return NULL;
    struct ListNode* end = pHead;
    struct ListNode* p = end->next;
    // 把p放在最前面，实现倒序 
    // 1.end的next指向p的next 
    // 2.把head放到p之后
    while(p != NULL) {
        end->next = p->next;
        p->next = pHead;
        
        pHead = p;
        p = end->next;
    }
    return pHead;
}

void printListNode(struct ListNode* pHead) {
    struct ListNode *p = pHead;
    while(p != NULL) {
        printf("%d ", p->val);
        p = p->next;
    }
    printf("\n");
}

int main() {
    
    ListNode pHead;
    pHead.val = 1;
    ListNode node2;
    node2.val = 2;
    ListNode node3;
    node3.val = 3;
    node3.next = NULL;
    
    pHead.next = &node2;
    node2.next = &node3;
    printListNode(&pHead);
     
    struct ListNode*head = ReverseList(&pHead);
    printListNode(head);
    
    return 0;
}