LeetCode in Erlang
206. Reverse Linked List
Easy
Given the head of a singly linked list, reverse the list, and return the reversed list.
Example 1:
Input: head = [1,2,3,4,5]
Output: [5,4,3,2,1]
Example 2:
Input: head = [1,2]
Output: [2,1]
Example 3:
Input: head = []
Output: []
Constraints:
- The number of nodes in the list is the range
[0, 5000]. -5000 <= Node.val <= 5000
Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?
Solution
%% Definition for singly-linked list.
%%
%% -record(list_node, {val = 0 :: integer(),
%% next = null :: 'null' | #list_node{}}).
-spec reverse_list(Head :: #list_node{} | null) -> #list_node{} | null.
reverse_list(null) -> null;
reverse_list(#list_node{val=V, next=Next}) -> reverse_list(Next, #list_node{val=V, next=null}).
reverse_list(null, Acc) -> Acc;
reverse_list(#list_node{val=V,next=Next}, Acc) -> reverse_list(Next, #list_node{val=V, next=Acc}).