vault backup: 2022-09-08 16:18:59

OJ notes/OJ-index.md

@@ -18,7 +18,7 @@ This is where I store notes about CS
 #### Collection of problems of same kind
 
 ```query
-#problem_collection 
+#problem_collection
 ```
 
 #### TODO

OJ notes/pages/Breadth First Search.md

@@ -12,7 +12,7 @@
 >
 > ##### Difficulty:
 >
-> #CS_analysis #difficulty_
+> #CS*analysis #difficulty*
 >
 > ##### Additional tags:
 

OJ notes/pages/Elementary Math Problems.md

@@ -3,10 +3,10 @@
 2022-09-08 15:23
 
 #math
-#algorithm 
+#algorithm
 #problem_collection
 
-These are problems solved by re-implementing elementary 
+These are problems solved by re-implementing elementary
 math:
 
 ### Add
@@ -18,5 +18,4 @@ math:
 
 ### Multiply
 
-
+### Divide
-### Divide

OJ notes/pages/Floyd's Cycle Finding Algorithm.md

@@ -46,7 +46,7 @@ While traversing the linked list one of these things will occur-
 - Move the fast pointer by **two** positions.
 - If both pointers meet at some point then a loop exists and if the fast pointer meets the end position then no loop exists.
 
-Example: 
+Example:
 [[Leetcode Linked-List-Cycle]]
 
 #### Part 2. **Locating the start** of the loop
@@ -98,7 +98,7 @@ Let us consider an example:
 - Move one step at a time until they met.
 - The start of the loop is where they met
 
-Example: 
+Example:
 [[Leetcode Linked-List-Cycle-II]]
 
 #### Example

OJ notes/pages/Leetcode Add-Two-Numbers.md

@@ -8,7 +8,7 @@
 >
 > ##### Data structures:
 >
-> #DS #linked_list 
+> #DS #linked_list
 >
 > ##### Difficulty:
 >
@@ -16,7 +16,7 @@
 >
 > ##### Additional tags:
 >
-> #leetcode 
+> #leetcode
 >
 > ##### Revisions:
 >
@@ -62,9 +62,9 @@ You may assume the two numbers do not contain any leading zero, except the numbe
 
 #### Constraints
 
--   The number of nodes in each linked list is in the range `[1, 100]`.
+- The number of nodes in each linked list is in the range `[1, 100]`.
--   `0 <= Node.val <= 9`
+- `0 <= Node.val <= 9`
--   It is guaranteed that the list represents a number that does not have leading zeros.
+- It is guaranteed that the list represents a number that does not have leading zeros.
 
 ### Thoughts
 
@@ -132,4 +132,4 @@ public:
     return ans;
   }
 };
-```
+```

OJ notes/pages/Leetcode Binary-Tree-Postorder-Traversal.md

@@ -12,7 +12,7 @@
 >
 > ##### Difficulty:
 >
-> #coding_problem #difficulty_
+> #coding*problem #difficulty*
 >
 > ##### Additional tags:
 >

OJ notes/pages/Leetcode Intersection-of-Two-Linked-Lists.md

@@ -0,0 +1,152 @@
+# Leetcode Intersection-of-Two-Linked-Lists
+
+2022-09-08 16:13
+
+> ##### Algorithms:
+>
+> #algorithm #two_pointers
+>
+> ##### Data structures:
+>
+> #DS #linked_list #set
+>
+> ##### Difficulty:
+>
+> #coding_problem #difficulty-easy
+>
+> ##### Additional tags:
+>
+> #leetcode
+>
+> ##### Revisions:
+>
+> N/A
+
+##### Links:
+
+- [Link to problem](https://leetcode.com/problems/intersection-of-two-linked-lists/)
+
+---
+
+### Problem
+
+Given the heads of two singly linked-lists `headA` and `headB`, return _the node at which the two lists intersect_. If the two linked lists have no intersection at all, return `null`.
+
+For example, the following two linked lists begin to intersect at node `c1`:
+
+![](https://assets.leetcode.com/uploads/2021/03/05/160_statement.png)
+
+The test cases are generated such that there are no cycles anywhere in the entire linked structure.
+
+**Note** that the linked lists must **retain their original structure** after the function returns.
+
+**Custom Judge:**
+
+The inputs to the **judge** are given as follows (your program is **not** given these inputs):
+
+- `intersectVal` - The value of the node where the intersection occurs. This is `0` if there is no intersected node.
+- `listA` - The first linked list.
+- `listB` - The second linked list.
+- `skipA` - The number of nodes to skip ahead in `listA` (starting from the head) to get to the intersected node.
+- `skipB` - The number of nodes to skip ahead in `listB` (starting from the head) to get to the intersected node.
+
+The judge will then create the linked structure based on these inputs and pass the two heads, `headA` and `headB` to your program. If you correctly return the intersected node, then your solution will be **accepted**.
+
+#### Examples
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2021/03/05/160_example_1_1.png)
+
+**Input:** intersectVal = 8, listA = [4,1,8,4,5], listB = [5,6,1,8,4,5], skipA = 2, skipB = 3
+**Output:** Intersected at '8'
+**Explanation:** The intersected node's value is 8 (note that this must not be 0 if the two lists intersect).
+From the head of A, it reads as [4,1,8,4,5]. From the head of B, it reads as [5,6,1,8,4,5]. There are 2 nodes before the intersected node in A; There are 3 nodes before the intersected node in B.
+
+- Note that the intersected node's value is not 1 because the nodes with value 1 in A and B (2nd node in A and 3rd node in B) are different node references. In other words, they point to two different locations in memory, while the nodes with value 8 in A and B (3rd node in A and 4th node in B) point to the same location in memory.
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2021/03/05/160_example_2.png)
+
+**Input:** intersectVal = 2, listA = [1,9,1,2,4], listB = [3,2,4], skipA = 3, skipB = 1
+**Output:** Intersected at '2'
+**Explanation:** The intersected node's value is 2 (note that this must not be 0 if the two lists intersect).
+From the head of A, it reads as [1,9,1,2,4]. From the head of B, it reads as [3,2,4]. There are 3 nodes before the intersected node in A; There are 1 node before the intersected node in B.
+
+**Example 3:**
+
+![](https://assets.leetcode.com/uploads/2021/03/05/160_example_3.png)
+
+**Input:** intersectVal = 0, listA = [2,6,4], listB = [1,5], skipA = 3, skipB = 2
+**Output:** No intersection
+**Explanation:** From the head of A, it reads as [2,6,4]. From the head of B, it reads as [1,5]. Since the two lists do not intersect, intersectVal must be 0, while skipA and skipB can be arbitrary values.
+Explanation: The two lists do not intersect, so return null.
+
+#### Constraints
+
+- The number of nodes of `listA` is in the `m`.
+- The number of nodes of `listB` is in the `n`.
+- `1 <= m, n <= 3 * 104`
+- `1 <= Node.val <= 105`
+- `0 <= skipA < m`
+- `0 <= skipB < n`
+- `intersectVal` is `0` if `listA` and `listB` do not intersect.
+- `intersectVal == listA[skipA] == listB[skipB]` if `listA` and `listB` intersect.
+
+### Thoughts
+
+> [!summary]
+> This can be solved using #two_pointers or #set
+
+#### Set
+
+Record the address of visited node iterating over `listA`,
+and verify if the address has been visited when iterating
+over `listB`
+
+#### Two pointers
+
+#TODO Use two pointers method to solve
+
+### Solution
+
+#### Set
+
+```cpp
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+class Solution {
+public:
+  ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
+    // O(M + N), using set.
+    unordered_set<ListNode *> used;
+
+    ListNode *ptrA = headA;
+
+    while (ptrA) {
+      used.insert(ptrA);
+      ptrA = ptrA->next;
+    }
+
+    ListNode *ptrB = headB;
+
+    while (ptrB) {
+      if (used.find(ptrB) != used.end()) {
+        // intersect
+        return ptrB;
+      }
+
+      ptrB = ptrB->next;
+    }
+
+    return nullptr;
+  }
+};
+```

OJ notes/pages/Leetcode Linked-List-Cycle-II.md

@@ -4,11 +4,11 @@
 
 > ##### Algorithms:
 >
-> #algorithm #Floyd_s_cycle_finding_algorithm 
+> #algorithm #Floyd_s_cycle_finding_algorithm
 >
 > ##### Data structures:
 >
-> #DS #linked_list 
+> #DS #linked_list
 >
 > ##### Difficulty:
 >
@@ -16,7 +16,7 @@
 >
 > ##### Additional tags:
 >
-> #leetcode 
+> #leetcode
 >
 > ##### Revisions:
 >
@@ -64,9 +64,9 @@ There is a cycle in a linked list if there is some node in the list that can be
 
 #### Constraints
 
--   The number of the nodes in the list is in the range `[0, 104]`.
+- The number of the nodes in the list is in the range `[0, 104]`.
--   `-105 <= Node.val <= 105`
+- `-105 <= Node.val <= 105`
--   `pos` is `-1` or a **valid index** in the linked-list.
+- `pos` is `-1` or a **valid index** in the linked-list.
 
 ### Thoughts
 
@@ -124,4 +124,4 @@ public:
     }
   }
 };
-```
+```

OJ notes/pages/Leetcode Longest-Palindrome.md

@@ -30,7 +30,7 @@
 
 ### Problem
 
-Given a string `s` which consists of lowercase or uppercase letters, return *the length of the **longest palindrome*** that can be built with those letters.
+Given a string `s` which consists of lowercase or uppercase letters, return \*the length of the **longest palindrome\*** that can be built with those letters.
 
 Letters are **case sensitive**, for example, `"Aa"` is not considered a palindrome here.
 

OJ notes/pages/Leetcode Pascal's-Triangle-II.md

@@ -61,7 +61,7 @@ In **Pascal's triangle**, each number is the sum of the two numbers directly abo
 
 > [!summary]
 > This is a #recursion problem.
-> 
+>
 > Follow up of [[Leetcode Pascal's-Triangle]]
 
 Because to get the nth row, we have to get the `n - 1` th