vault backup: 2022-06-15 22:12:54

CS notes/CS-index.md

@@ -30,6 +30,7 @@ tag:#leetcode
 - [[Leetcode Merge-Two-Sorted-Lists]]
 - [[Leetcode Pascal's-Triangle]]
 - [[Leetcode Ransom-Note]]
+- [[Leetcode Remove-Linked-List-Elements]]
 - [[Leetcode Reshape-The-Matrix]]
 - [[Leetcode Search-a-2D-Matrix]]
 - [[Leetcode Two-Sum]]
@@ -66,6 +67,7 @@ tag:#DS tag:#coding_problem -tag:#template_remove_me
 - [[Leetcode Merge-Two-Sorted-Lists]]
 - [[Leetcode Pascal's-Triangle]]
 - [[Leetcode Ransom-Note]]
+- [[Leetcode Remove-Linked-List-Elements]]
 - [[Leetcode Reshape-The-Matrix]]
 - [[Leetcode Search-a-2D-Matrix]]
 - [[Leetcode Two-Sum]]
@@ -80,6 +82,7 @@ tag:#DS tag:#CS_analysis -tag:#template_remove_me
 - [[$filename]]
 ```
  
+- [[Binary Search Algorithm.sync-conflict-20220615-121016-T44CT3O]]
 - [[cpp_Range_based_for_loop]]
 - [[cpp_std_multiset]]
 - [[cpp_std_unordered_map]]
@@ -118,11 +121,5 @@ tag:#algorithm tag:#CS_analysis -tag:#template_remove_me
 - [[$filename]]
 ```
 
-- [[Binary Search Algorithm]]
-- [[cpp_std_sort]]
-- [[Floyd's Cycle Finding Algorithm]]
-- [[Kadane's Algorithm]]
-- [[Two pointers approach]]
- 
 
  

CS notes/pages/Leetcode Remove-Linked-List-Elements.md

@@ -3,33 +3,145 @@
 #### 2022-06-15 21:50
 
 ---
-##### Algorithms:
-#algorithm 
 ##### Data structures:
-#DS
+#DS #linked_list 
 ##### Difficulty:
-#<CHANGE_ME> #coding_problem #difficulty-easy 
+#leetcode #coding_problem #difficulty-easy 
 ##### Related topics:
 ```expander
-tag:#<INSERT_TAG_HERE>
+tag:#linked_list
 ```
  
+- [[Floyd's Cycle Finding Algorithm]]
+- [[Leetcode Linked-List-Cycle]]
+- [[Leetcode Merge-Two-Sorted-Lists]]
+- [[Two pointers approach]]
  
 
 ##### Links:
-- [Link to problem]()
+- [Link to problem](https://leetcode.com/problems/remove-linked-list-elements/)
+- [Additional Solutions](https://leetcode.com/problems/remove-linked-list-elements/discuss/722528/C++-2-solutions:-With-single-pointer-+-With-double-pointers-(Easy-to-understand)/1390186)
 ___
 ### Problem
+Given the `head` of a linked list and an integer `val`, remove all the nodes of the linked list that has `Node.val == val`, and return _the new head_.
 
 #### Examples
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2021/03/06/removelinked-list.jpg)
+
 ```markdown
+**Input:** head = [1,2,6,3,4,5,6], val = 6
+**Output:** [1,2,3,4,5]
 ```
 
+**Example 2:**
+
+```markdown
+**Input:** head = [], val = 1
+**Output:** []
+```
+
+**Example 3:**
+
+```markdown
+**Input:** head = [7,7,7,7], val = 7
+**Output:** []
+```
 #### Constraints
+-   The number of nodes in the list is in the range `[0, 104]`.
+-   `1 <= Node.val <= 50`
+-   `0 <= val <= 50`
 
 ### Thoughts
 
-> [!summary]
-> This is a #template_remove_me
-
+Simple linked list operations, but remember to check for special cases:
+- The pointer is null
 ### Solution
+
+Two pointers, O(n)
+```cpp
+/**
+ * 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:
+  ListNode *removeElements(ListNode *head, int val) {
+    // O(n)
+    while (head != NULL && head->val == val) {
+      head = head->next;
+    }
+
+    ListNode *before = NULL;
+    ListNode *ptr = head;
+    ListNode *tmp;
+
+    while (ptr != NULL) {
+      if (ptr->val == val) {
+        if (before != NULL) {
+          before->next = ptr->next;
+        }
+
+        // delete ptr and change ptr to ptr->next
+        tmp = ptr->next;
+        delete ptr;
+        ptr = tmp;
+      } else {
+        before = ptr;
+        ptr = ptr->next;
+      }
+    }
+    return head;
+  }
+};
+```
+
+These two are taken from discussions, and they are **not** memory safe.
+Recursive solution from the same guy:
+```cpp
+class Solution {
+public:
+  ListNode *removeElements(ListNode *head, int val) {
+    // Base situation
+    if (head == NULL)
+      return NULL;
+    // Change head->next by it's val (if no val found, will not be changed)
+    head->next = removeElements(head->next, val);
+    // Return head or head->next, depending on the val.
+    // If matched val, return its next, effectively deleting the node.
+    return (head->val == val) ? head->next : head;
+  }
+};
+```
+
+One pointer from [Discussions](https://leetcode.com/problems/remove-linked-list-elements/discuss/722528/C++-2-solutions:-With-single-pointer-+-With-double-pointers-(Easy-to-understand)/1390186)
+```cpp
+class Solution {
+public:
+  ListNode *removeElements(ListNode *head, int val) {
+    while (head != NULL && head->val == val)
+      head = head->next;
+
+    // He checked NULL here, so he doesn't have to check in while loop
+    if (head == NULL)
+      return head;
+
+    ListNode *res = head;
+    while (head->next != NULL) {
+      if (head->next->val == val)
+        head->next = head->next->next;
+      else
+        head = head->next;
+    }
+    return res;
+  }
+};
+```
+

CS notes/pages/Leetcode Reverse-Linked-List.md

@@ -0,0 +1,35 @@
+# Leetcode Reverse-Linked-List
+
+#### 2022-06-15 22:07
+
+---
+##### Algorithms:
+#algorithm #recursion 
+##### Data structures:
+#DS #linked_list 
+##### Difficulty:
+#leetcode  #coding_problem #difficulty-easy 
+##### Related topics:
+```expander
+tag:#linked_list
+```
+ 
+ 
+
+##### Links:
+- [Link to problem]()
+___
+### Problem
+
+#### Examples
+```markdown
+```
+
+#### Constraints
+
+### Thoughts
+
+> [!summary]
+> This is a #template_remove_me
+
+### Solution