WiP: solution for neetcode task

leetcode/linked_lists/0206_reverse_linked_list.py

@@ -0,0 +1,74 @@
+from typing import Optional
+import pytest
+# Definition for singly-linked list.
+
+
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+    def __repr__(self) -> str:
+        return f"Val: {self.val}"
+
+
+# Not solved by me
+class Solution:
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        rl = []
+        if not head:
+            return
+
+        def rr(cn: ListNode):
+            if cn.next:
+                rr(cn.next)
+                cn.next.next = cn
+                rl.append(cn)
+            else:
+                rl.append(cn)
+
+        rr(head)
+        head.next = None
+
+class SolutionFromLeetCode:
+    def reverseList(self, head: ListNode) -> ListNode:
+        # Initialize pointers
+        prev = None  # Previous node starts as None
+        curr = head  # Current node starts at the head
+
+        # Traverse the list
+        while curr is not None:
+            next_node = curr.next  # Save the next node
+            
+            curr.next = prev  # Reverse the link
+            
+            # Move pointers forward
+            prev = curr  # Move prev to the current node
+            curr = next_node  # Move curr to the next node
+
+        # prev is now the new head of the reversed list
+        return prev
+
+
+def test_solution():
+    l5 = ListNode(val=5, next=None)
+    l4 = ListNode(val=4, next=l5)
+    l3 = ListNode(val=3, next=l4)
+    l2 = ListNode(val=2, next=l3)
+    l1 = ListNode(val=1, next=l2)
+    sol = SolutionFromLeetCode()
+    sol.reverseList(head=l1)
+    assert l1.next is None
+    assert l2.next == l1
+    assert l3.next == l2
+    assert l4.next == l3
+    assert l5.next == l4
+
+
+def test_solution_1():
+    l2 = ListNode(val=2, next=None)
+    l1 = ListNode(val=1, next=l2)
+    sol = SolutionFromLeetCode()
+    sol.reverseList(head=l1)
+    assert l1.next is None
+    assert l2.next == l1

neetcode/arrays/encode_decode_strings.py

@@ -0,0 +1,49 @@
+##################### Section ##############################
+# Section topic: Arrays
+#
+# Design an algorithm to encode a list of strings to a single string. The encoded string is then decoded back to the original list of strings.
+#
+# Please implement encode and decode
+#
+# Example 1:
+#
+# Input: ["neet","code","love","you"]
+#
+# Output:["neet","code","love","you"]
+# Example 2:
+#
+# Input: ["we","say",":","yes"]
+#
+# Output: ["we","say",":","yes"]
+# Constraints:
+#
+# 0 <= strs.length < 100
+# 0 <= strs[i].length < 200
+# strs[i] contains only UTF-8 characters.
+#
+############################################################
+from typing import List
+
+
+class Solution:
+    def encode(self, strs: List[str]) -> str:
+        delim: str = "-+-"
+        res: str = ""
+        counts: str = ""
+        encoded: str = ""
+        for elem in strs:
+            counts += f"{len(elem)}{delim}"
+            encoded += elem
+        counts += delim
+        res = counts + encoded
+        return encoded
+
+
+    def decode(self, s: str) -> List[str]:
+        pass
+
+
+s = Solution()
+
+print(s.encode(strs=["we", "say", ":", "yes"]))
+# s.decode("we say: yes")

neetcode/arrays/encode_decode_strings/encode_decode_strings.py

@@ -0,0 +1,53 @@
+##################### Section ##############################
+# Section topic: Arrays
+#
+# Design an algorithm to encode a list of strings to a single string. The encoded string is then decoded back to the original list of strings.
+#
+# Please implement encode and decode
+#
+# Example 1:
+#
+# Input: ["neet","code","love","you"]
+#
+# Output:["neet","code","love","you"]
+# Example 2:
+#
+# Input: ["we","say",":","yes"]
+#
+# Output: ["we","say",":","yes"]
+# Constraints:
+#
+# 0 <= strs.length < 100
+# 0 <= strs[i].length < 200
+# strs[i] contains only UTF-8 characters.
+#
+############################################################
+from typing import List
+
+
+class Solution:
+    delim: str = "-+-"
+
+    def encode(self, strs: List[str]) -> str:
+        delim: str = self.delim
+        res: str = ""
+        counts: str = ""
+        encoded: str = ""
+        for elem in strs:
+            counts += f"{len(elem)}{delim}"
+            encoded += elem
+        counts += delim
+        res = counts + encoded
+        return res
+
+    def decode(self, s: str) -> List[str]:
+        splitted = s.split(f"{self.delim}{self.delim}")
+        breaks = [int(s) for s in splitted[0].split(self.delim)]
+        res = []
+        return breaks
+
+
+s = Solution()
+
+en = s.encode(strs=["we", "say", ":", "yes"])
+print(s.decode(en))