02_Remove_Nth_Node_end.cpp

// Given the head of a linked list, remove the nth node from the end of the list and return its head.

// Example 1:

// Input: head = [1,2,3,4,5], n = 2
// Output: [1,2,3,5]
// Example 2:

// Input: head = [1], n = 1
// Output: []
// Example 3:

// Input: head = [1,2], n = 1
// Output: [1]






// Geeksforgeeks help 

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        int k = 0;
        ListNode* curr = head;
        while (curr != nullptr) {
            curr = curr->next;
            k++;
        }
        if (k-n == 0) return head->next;
        curr = head;
        for (int i=1; i<k-n; i++) {
            curr = curr->next;
        }
        curr->next = curr->next->next;

        return head;
    }
};