LeetCode in Erlang
24. Swap Nodes in Pairs
Medium
Given a linked list, swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list’s nodes (i.e., only nodes themselves may be changed.)
Example 1:
Input: head = [1,2,3,4]
Output: [2,1,4,3]
Example 2:
Input: head = []
Output: []
Example 3:
Input: head = [1]
Output: [1]
Constraints:
- The number of nodes in the list is in the range
[0, 100]. 0 <= Node.val <= 100
Solution
%% Definition for singly-linked list.
%%
%% -record(list_node, {val = 0 :: integer(),
%% next = null :: 'null' | #list_node{}}).
%% Swap every two adjacent nodes in a linked list
-spec swap_pairs(Head :: #list_node{} | null) -> #list_node{} | null.
swap_pairs(null) -> null;
swap_pairs(#list_node{next = null} = Head) -> Head;
swap_pairs(First = #list_node{next = Second}) ->
NextPair = Second#list_node.next,
% Connect second node to first
Second#list_node{
next = First#list_node{
% Connect first node to result of swapping remaining pairs
next = swap_pairs(NextPair)
}
}.