19.remove-nth-node-from-end-of-list.cpp

/*
 * @lc app=leetcode id=19 lang=cpp
 *
 * [19] Remove Nth Node From End of List
 *
 * https://leetcode.com/problems/remove-nth-node-from-end-of-list/description/
 *
 * algorithms
 * Medium (34.02%)
 * Total Accepted:    358.7K
 * Total Submissions: 1.1M
 * Testcase Example:  '[1,2,3,4,5]\n2'
 *
 * Given a linked list, remove the n-th node from the end of list and return
 * its head.
 * 
 * Example:
 * 
 * 
 * Given linked list: 1->2->3->4->5, and n = 2.
 * 
 * After removing the second node from the end, the linked list becomes
 * 1->2->3->5.
 * 
 * 
 * Note:
 * 
 * Given n will always be valid.
 * 
 * Follow up:
 * 
 * Could you do this in one pass?
 * 
 */
/**
 * Definition for singly-linked list.
 */
// #include<bits/stdc++.h>
// using namespace std;
// struct ListNode {
//     int val;
//     ListNode *next;
//     ListNode(int x) : val(x), next(NULL) {}
// };
 

class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        int i=0;
        if(head->next==NULL){
            return NULL;
        }
        ListNode *det=head,*temp=head;
        while(temp->next !=NULL){
            temp = temp->next;
            i++;
            if(i>n) det = det->next;
        } 
        if(i+1==n) head=head->next;
        else det->next = det->next->next;
        return head;
    }
    }
};