C++基础知识（六）链表等

• 求链表中倒数第k个节点

/*
struct ListNode {
	int val;
	struct ListNode *next;
	ListNode(int x) :
			val(x), next(NULL) {
	}
};*/

class Solution {
public:
    ListNode* FindKthToTail(ListNode* pListHead, unsigned int k) {
        if(pListHead==NULL)return NULL;
        ListNode* p=pListHead;
        ListNode* q=pListHead;
        while(k-->0){
            p=p->next;
            if(p==NULL && k==0) return pListHead; //链表长度等于k
            if(p==NULL)return NULL; //链表长度小于k
        }
        while(p!=NULL){
            p=p->next;
            q=q->next;
        }
        return q;
        
        /*
        if(pListHead==NULL)return NULL;
        int count=0;
        ListNode* p=pListHead;
        while(p!=NULL){
            p=p->next;
            count++;
        }
        if(k>count)return NULL;
        else{
            p=pListHead;
            int i=0;
            while(i < count-k){
                p=p->next;
                i++;
            }
            return p;
        }
        */
        
    }
};

• 链表反转

/*
struct ListNode {
	int val;
	struct ListNode *next;
	ListNode(int x) :
			val(x), next(NULL) {
	}
};*/
class Solution {
public:
    ListNode* ReverseList(ListNode* pHead) {
        if(pHead == NULL)return NULL;
        if(pHead->next == NULL)return pHead;
        if(pHead->next->next == NULL){
            ListNode *p = pHead->next->next; 
            pHead->next->next = pHead->next;
            pHead->next = NULL;
            return p;
        }
        
        ListNode *l, *p, *r;
        l = pHead;
        p = pHead->next;
        r = pHead->next->next;
        while(r != NULL){
            p->next = l;
            l=p;
            p=r;
            r=r->next;
        }
        p->next = l;
        pHead -> next = NULL;
        return p;
    }
};