day 1

Author: sachuverma

Leetcode Daily Challenge/April-2021/01. Palindrome Linked List.cpp

@@ -0,0 +1,71 @@
+/*
+Palindrome Linked List
+======================
+
+Given the head of a singly linked list, return true if it is a palindrome.
+
+Example 1:
+Input: head = [1,2,2,1]
+Output: true
+
+Example 2:
+Input: head = [1,2]
+Output: false
+
+Constraints:
+The number of nodes in the list is in the range [1, 105].
+0 <= Node.val <= 9
+
+Follow up: Could you do it in O(n) time and O(1) space?
+*/
+
+/**
+ * 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:
+  bool isPalindrome(ListNode *head)
+  {
+    auto slow = head, fast = head;
+    while (fast && fast->next)
+    {
+      slow = slow->next;
+      fast = fast->next->next;
+    }
+    auto head2 = reverse(slow);
+    auto head1 = head;
+    while (head2 && head1)
+    {
+      if (head1->val != head2->val)
+        return false;
+      head1 = head1->next;
+      head2 = head2->next;
+    }
+    return true;
+  }
+
+  ListNode *reverse(ListNode *mid)
+  {
+    if (!mid || !mid->next)
+      return mid;
+    auto curr = mid, next = curr->next;
+    curr->next = NULL;
+    while (next)
+    {
+      auto nextNext = next->next;
+      next->next = curr;
+      curr = next;
+      next = nextNext;
+    }
+
+    return curr;
+  }
+};

Leetcode Daily Challenge/April-2021/README.md

@@ -0,0 +1,5 @@
+# April 2021 LeetCoding Challenge
+
+| Day | Question Links                                                                                                                         |                Solutions                |
+| :-: | :------------------------------------------------------------------------------------------------------------------------------------- | :-------------------------------------: |
+| 1.  | [Palindrome Linked List](https://leetcode.com/explore/featured/card/april-leetcoding-challenge-2021/593/week-1-april-1st-april-7th/3693/) | [cpp](./01.%20Palindrome%20Linked%20List.cpp) |

Leetcode Daily Challenge/README.md

@@ -7,6 +7,8 @@
 - [December](./December-2020)
 
 ### 2021
+
 - [January](./January-2021)
 - [February](./February-2021)
-- [March](./March-2021)
+- [March](./March-2021)
+- [April](./April-2021)

README.md

@@ -165,16 +165,26 @@ Urls for other Notes, and Reading Resources picked from different editorials.
 - [📘 CPP Syntax Cheet Sheet](./Resources/Articles/CPP-SYNTAX.md)
 </details>
 
+<details>
+  <summary>Last Minute Notes</summary>
+
+- [📙 Last Minute Notes – Operating Systems](https://www.geeksforgeeks.org/last-minute-notes-operating-systems/)
+- [📙 Last Minute Notes – Computer Networks](https://www.geeksforgeeks.org/last-minute-notes-computer-network/)
+- [📙 Last Minute Notes – DBMS](https://www.geeksforgeeks.org/last-minute-notes-dbms/)
+- [📙 Last Minute Notes – Algorithms](https://www.geeksforgeeks.org/lmns-algorithms-gq/)
+- [📙 Last Minute Notes – Data Structure](https://www.geeksforgeeks.org/lmns-gq/lmns-data-structure-gq/)
+</details>
+
 <details>
   <summary>Notes/Question/Explanations</summary>
 
-  - [📒 Dynamic Programming and Bit Masking](./Resources/Notes/Dynamic%20Programming%20and%20Bit%20Masking.md)
-  - [📒 Disjoint Set Union (Union Find)](./Resources/Notes/Disjoint%20Set%20Union.md)
-  - [📒 Ternary Search](./Resources/Notes/Ternary%20Search.md)
-  - [📒 Binary Search for Beginners (leetcode)](https://leetcode.com/discuss/general-discussion/691825/Binary-Search-for-Beginners-Problems-or-Patterns-or-Sample-solutions)
-  - [📕 Dynamic Programming (questions)](./Resources/Questions/Dynamic-Programming.md)
-  - [📕 Union Find (questions)](./Resources/Questions/Union-Find.md)
-  - [📕 Ternary Search (questions)](./Resources/Questions/Ternary-Search.md)
+- [📒 Dynamic Programming and Bit Masking](./Resources/Notes/Dynamic%20Programming%20and%20Bit%20Masking.md)
+- [📒 Disjoint Set Union (Union Find)](./Resources/Notes/Disjoint%20Set%20Union.md)
+- [📒 Ternary Search](./Resources/Notes/Ternary%20Search.md)
+- [📒 Binary Search for Beginners (leetcode)](https://leetcode.com/discuss/general-discussion/691825/Binary-Search-for-Beginners-Problems-or-Patterns-or-Sample-solutions)
+- [📕 Dynamic Programming (questions)](./Resources/Questions/Dynamic-Programming.md)
+- [📕 Union Find (questions)](./Resources/Questions/Union-Find.md)
+- [📕 Ternary Search (questions)](./Resources/Questions/Ternary-Search.md)
 </details>
 
 <br />