假期打卡第七天

利用两个指针向后走，只要相遇就是一个环，遇不上就不是一个环

bool hasCycle(ListNode *head) {
    
    
    if(head == NULL) return false;
    if(head->next == NULL) return false;
    if(head == head->next) return true;
    ListNode *slow = head;
    ListNode *fast = head;
    while(fast->next != NULL && fast->next->next != NULL){
    
    
	    slow = slow->next;
	    fast = fast->next->next;
	    if(slow == fast) return true;
    }
    return false;
}

两数相加
新建一片内存空间之后加起来，存入，进位存入int中

ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
    
    
    ListNode *OCC = new ListNode(0);
    ListNode *count1 = l1,*count2 = l2;
    ListNode *tmp = OCC;
    int out = 0;
    while(count1 != nullptr && count2 != nullptr) {
    
    
        tmp->next = new ListNode((count1->val + count2->val + out) % 10);
        tmp = tmp->next;
        out = (count1->val + count2->val + out) / 10;
        count1 = count1->next;
        count2 = count2->next;
    }
    while(count1 != nullptr) {
    
    
        tmp->next = new ListNode((count1->val + out) % 10);
        tmp = tmp->next;
        out = (count1->val + out) / 10;
        count1 = count1->next;
    }
    while(count2 != nullptr) {
    
    
        tmp->next = new ListNode((count2->val + out) % 10);
        tmp = tmp->next;
        out = (count2->val + out) / 10;
        count2 = count2->next;
    }
    if(out != 0) tmp->next = new ListNode(out);
    return OCC->next;
}