spring中常用注解

题目描述

法一）计算链表长度

class Solution {
public:
    int getLength(ListNode* head){
		int len=0;
		while(head){
			++len;
			head =head->next;
		}
		return len;
	}

    ListNode* removeNthFromEnd(ListNode* head, int n) {
        int len = getLength(head);
		ListNode* dummy = new ListNode (0, head);   //0表示结点值，head表示下一个结点
		ListNode* cur = dummy;
		for(int i=1;i<len-n+1;i++){
			cur = cur->next;
		}
		cur->next = cur->next->next;
		ListNode* ans = dummy->next;
		delete dummy;
		return ans;
    }
};

法二）栈

class Solution{
public:
	ListNode* removeNthFromEnd(ListNode* head, int n){
		stack<ListNode*> stk;
		ListNode* dummy = new ListNode(0, head);
		ListNode* cur = dummy;
		while(cur){
			stk.push(cur);
			cur = cur->next;
		}
		for(int i=0;i<n;i++){
			stk.pop();
		}
		ListNode* prev = stk.top();
		prev->next = prev->next->next;
		ListNode* ans = dummy->next;
        delete dummy;
        return ans; 
	}
};

法三）双指针

class Solution{
public:
	ListNode* removeNthFromEnd(ListNode* head, int n){
		ListNode* dummy = new ListNode(0, head);
		ListNode* first = head;
		ListNode* second = dummy;
		for(int i=0;i<n;i++){
			first = first->next;
		}
		
		while(first){
			first = first->next;
			second = second->next;
		}
		second->next = second->next->next;
		ListNode* ans = dummy->next;
		delete dummy;
		return ans;
	}
};