Add solution for LL: remove n'th node from end of LL

neetcode/linked_list/remove_node_from_end_of_linked_list/README.md

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+# Remove Node From End of Linked List
+
+You are given the beginning of a linked list head, and an integer n.
+
+Remove the nth node from the end of the list and return the beginning of the list.
+
+Example 1:
+
+Input: head = [1,2,3,4], n = 2
+
+Output: [1,2,4]
+Example 2:
+
+Input: head = [5], n = 1
+
+Output: []
+Example 3:
+
+Input: head = [1,2], n = 2
+
+Output: [2]
+Constraints:
+
+The number of nodes in the list is sz.
+1 <= sz <= 30
+0 <= Node.val <= 100
+1 <= n <= sz
+
+# Edge cases
+## size of LL == 1
+return None
+
+## n = 1 
+return head.next
+
+# Solution
+- Save head and return it after algo

neetcode/linked_list/remove_node_from_end_of_linked_list/solution.py

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+from typing import List, Optional
+
+
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+
+class Solution:
+    def removeNthFromEnd(self, head: Optional[ListNode], n: int) -> Optional[ListNode]:
+        if not head:
+            return None
+        if head.next is None:
+            return None
+        perm_head = head
+        nodes = []
+        while head:
+            nodes.append(head)
+            head = head.next
+        if n == 1:
+            nodes[-2].next = None
+            return perm_head
+        if n == len(nodes):
+            return perm_head.next
+        counter = 1 
+        for i in range(len(nodes) - 1, 0, -1):
+            if counter == n:
+                nodes[i - 1].next = nodes[i + 1]
+            counter += 1
+        return perm_head
+
+
+if __name__ == "__main__":
+    s = Solution()
+    e3 = ListNode(3, None)
+    e2 = ListNode(2, e3)
+    e1 = ListNode(1, e2)
+    e0 = ListNode(0, e1)
+    fe = s.removeNthFromEnd(e0, 1)
+    while fe:
+        print(f"{fe.val}")
+        fe = fe.next

neetcode/linked_list/remove_node_from_end_of_linked_list/solution_iteration.py

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+from typing import List, Optional
+
+
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+
+class Solution:
+    def removeNthFromEnd(self, head: Optional[ListNode], n: int) -> Optional[ListNode]:
+        N = 0
+        cur = head
+        while cur:
+            N += 1
+            cur = cur.next
+
+        removeIndex = N - n
+        if removeIndex == 0:
+            return head.next
+
+        cur = head
+        for i in range(N - 1):
+            if (i + 1) == removeIndex:
+                cur.next = cur.next.next
+                break
+            cur = cur.next
+        return head
+
+
+if __name__ == "__main__":
+    s = Solution()
+    e3 = ListNode(3, None)
+    e2 = ListNode(2, e3)
+    e1 = ListNode(1, e2)
+    e0 = ListNode(0, e1)
+    fe = s.removeNthFromEnd(e0, 1)
+    while fe:
+        print(f"{fe.val}")
+        fe = fe.next