Added tasks 2001-2400

src/main/kotlin/g1901_2000/s1978_employees_whose_manager_left_the_company/readme.md

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+[![](https://img.shields.io/github/stars/javadev/LeetCode-in-Kotlin?label=Stars&style=flat-square)](https://github.com/javadev/LeetCode-in-Kotlin)
+[![](https://img.shields.io/github/forks/javadev/LeetCode-in-Kotlin?label=Fork%20me%20on%20GitHub%20&style=flat-square)](https://github.com/javadev/LeetCode-in-Kotlin/fork)
+
+## 1978\. Employees Whose Manager Left the Company
+
+Easy
+
+SQL Schema
+
+Table: `Employees`
+
+    +-------------+----------+ 
+    | Column Name | Type     | 
+    +-------------+----------+ 
+    | employee_id | int      | 
+    | name        | varchar  | 
+    | manager_id  | int      | 
+    | salary      | int      | 
+    +-------------+----------+ 
+
+employee_id is the primary key for this table. This table contains information about the employees, their salary, and the ID of their manager. Some employees do not have a manager (manager_id is null).
+
+Write an SQL query to report the IDs of the employees whose salary is strictly less than `$30000` and whose manager left the company. When a manager leaves the company, their information is deleted from the `Employees` table, but the reports still have their `manager_id` set to the manager that left.
+
+Return the result table ordered by `employee_id`.
+
+The query result format is in the following example.
+
+**Example 1:**
+
+**Input: ** Employees table: 
+
+    +-------------+-----------+------------+--------+ 
+    | employee_id | name      | manager_id | salary | 
+    +-------------+-----------+------------+--------+ 
+    | 3           | Mila      | 9          | 60301  | 
+    | 12          | Antonella | null       | 31000  | 
+    | 13          | Emery     | null       | 67084  | 
+    | 1           | Kalel     | 11         | 21241  | 
+    | 9           | Mikaela   | null       | 50937  | 
+    | 11          | Joziah    | 6          | 28485  | 
+    +-------------+-----------+------------+--------+
+
+**Output:** 
+
+    +-------------+ 
+    | employee_id | 
+    +-------------+ 
+    | 11          | 
+    +-------------+
+
+**Explanation:**
+
+The employees with a salary less than $30000 are 1 (Kalel) and 11 (Joziah). 
+
+Kalel's manager is employee 11, who is still in the company (Joziah).
+
+Joziah's manager is employee 6, who left the company because there is no row for employee 6 as it was deleted.
+
+## Solution
+
+```sql
+# Write your MySQL query statement below
+select employee_id from employees where manager_id not in (select distinct (employee_id) from employees)
+AND salary < 30000 order by employee_id
+```

src/main/kotlin/g2001_2100/s2001_number_of_pairs_of_interchangeable_rectangles/readme.md

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+[![](https://img.shields.io/github/stars/javadev/LeetCode-in-Kotlin?label=Stars&style=flat-square)](https://github.com/javadev/LeetCode-in-Kotlin)
+[![](https://img.shields.io/github/forks/javadev/LeetCode-in-Kotlin?label=Fork%20me%20on%20GitHub%20&style=flat-square)](https://github.com/javadev/LeetCode-in-Kotlin/fork)
+
+## 2001\. Number of Pairs of Interchangeable Rectangles
+
+Medium
+
+You are given `n` rectangles represented by a **0-indexed** 2D integer array `rectangles`, where <code>rectangles[i] = [width<sub>i</sub>, height<sub>i</sub>]</code> denotes the width and height of the <code>i<sup>th</sup></code> rectangle.
+
+Two rectangles `i` and `j` (`i < j`) are considered **interchangeable** if they have the **same** width-to-height ratio. More formally, two rectangles are **interchangeable** if <code>width<sub>i</sub>/height<sub>i</sub> == width<sub>j</sub>/height<sub>j</sub></code> (using decimal division, not integer division).
+
+Return _the **number** of pairs of **interchangeable** rectangles in_ `rectangles`.
+
+**Example 1:**
+
+**Input:** rectangles = \[\[4,8],[3,6],[10,20],[15,30]]
+
+**Output:** 6
+
+**Explanation:** The following are the interchangeable pairs of rectangles by index (0-indexed): 
+
+- Rectangle 0 with rectangle 1: 4/8 == 3/6. 
+
+- Rectangle 0 with rectangle 2: 4/8 == 10/20. 
+
+- Rectangle 0 with rectangle 3: 4/8 == 15/30. 
+
+- Rectangle 1 with rectangle 2: 3/6 == 10/20. 
+
+- Rectangle 1 with rectangle 3: 3/6 == 15/30. 
+
+- Rectangle 2 with rectangle 3: 10/20 == 15/30.
+
+**Example 2:**
+
+**Input:** rectangles = \[\[4,5],[7,8]]
+
+**Output:** 0
+
+**Explanation:** There are no interchangeable pairs of rectangles.
+
+**Constraints:**
+
+*   `n == rectangles.length`
+*   <code>1 <= n <= 10<sup>5</sup></code>
+*   `rectangles[i].length == 2`
+*   <code>1 <= width<sub>i</sub>, height<sub>i</sub> <= 10<sup>5</sup></code>
+
+## Solution
+
+```kotlin
+@Suppress("NAME_SHADOWING")
+class Solution {
+    private fun factorial(n: Long): Long {
+        var n = n
+        var m: Long = 0
+        while (n > 0) {
+            m += n
+            n -= 1
+        }
+        return m
+    }
+
+    fun interchangeableRectangles(rec: Array<IntArray>): Long {
+        val ratio = DoubleArray(rec.size)
+        for (i in rec.indices) {
+            ratio[i] = rec[i][0].toDouble() / rec[i][1]
+        }
+        ratio.sort()
+        var res: Long = 0
+        var k = 0
+        for (j in 0 until ratio.size - 1) {
+            if (ratio[j] == ratio[j + 1]) {
+                k++
+            }
+            if (ratio[j] != ratio[j + 1] || j + 2 == ratio.size) {
+                res += factorial(k.toLong())
+                k = 0
+            }
+        }
+        return res
+    }
+}
+```

src/main/kotlin/g2001_2100/s2002_maximum_product_of_the_length_of_two_palindromic_subsequences/readme.md

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+[![](https://img.shields.io/github/stars/javadev/LeetCode-in-Kotlin?label=Stars&style=flat-square)](https://github.com/javadev/LeetCode-in-Kotlin)
+[![](https://img.shields.io/github/forks/javadev/LeetCode-in-Kotlin?label=Fork%20me%20on%20GitHub%20&style=flat-square)](https://github.com/javadev/LeetCode-in-Kotlin/fork)
+
+## 2002\. Maximum Product of the Length of Two Palindromic Subsequences
+
+Medium
+
+Given a string `s`, find two **disjoint palindromic subsequences** of `s` such that the **product** of their lengths is **maximized**. The two subsequences are **disjoint** if they do not both pick a character at the same index.
+
+Return _the **maximum** possible **product** of the lengths of the two palindromic subsequences_.
+
+A **subsequence** is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters. A string is **palindromic** if it reads the same forward and backward.
+
+**Example 1:**
+
+![example-1](https://assets.leetcode.com/uploads/2021/08/24/two-palindromic-subsequences.png)
+
+**Input:** s = "leetcodecom"
+
+**Output:** 9
+
+**Explanation:** An optimal solution is to choose "ete" for the 1<sup>st</sup> subsequence and "cdc" for the 2<sup>nd</sup> subsequence.
+
+The product of their lengths is: 3 \* 3 = 9. 
+
+**Example 2:**
+
+**Input:** s = "bb"
+
+**Output:** 1
+
+**Explanation:** An optimal solution is to choose "b" (the first character) for the 1<sup>st</sup> subsequence and "b" (the second character) for the 2<sup>nd</sup> subsequence.
+
+The product of their lengths is: 1 \* 1 = 1. 
+
+**Example 3:**
+
+**Input:** s = "accbcaxxcxx"
+
+**Output:** 25
+
+**Explanation:** An optimal solution is to choose "accca" for the 1<sup>st</sup> subsequence and "xxcxx" for the 2<sup>nd</sup> subsequence.
+
+The product of their lengths is: 5 \* 5 = 25. 
+
+**Constraints:**
+
+*   `2 <= s.length <= 12`
+*   `s` consists of lowercase English letters only.
+
+## Solution
+
+```kotlin
+class Solution {
+    fun maxProduct(s: String): Int {
+        if (s.length == 2) {
+            return 1
+        }
+        val list: MutableList<State> = ArrayList()
+        val chars = s.toCharArray()
+        val visited: MutableSet<State> = HashSet()
+        for (i in chars.indices) {
+            val mask = 1 shl i
+            recur(chars, State(i, i, 0, mask), list, visited)
+            recur(chars, State(i, i + 1, 0, mask), list, visited)
+        }
+        list.sortWith { a: State, b: State -> b.cnt - a.cnt }
+        var res = 1
+        val explored: MutableSet<Int> = HashSet()
+        for (i in 0 until list.size - 1) {
+            if (explored.contains(i)) {
+                continue
+            }
+            val cur = list[i]
+            if (cur.cnt == 1) {
+                break
+            }
+            for (j in i + 1 until list.size) {
+                val cand = list[j]
+                if (cur.mask and cand.mask < 1) {
+                    if (explored.add(j)) {
+                        res = res.coerceAtLeast(cur.cnt * cand.cnt)
+                    }
+                    break
+                }
+            }
+        }
+        return res
+    }
+
+    private fun recur(chars: CharArray, s: State, list: MutableList<State>, visited: MutableSet<State>) {
+        if (s.i < 0 || s.j >= chars.size) {
+            return
+        }
+        if (!visited.add(s)) {
+            return
+        }
+        if (chars[s.i] == chars[s.j]) {
+            val m = s.mask or (1 shl s.i) or (1 shl s.j)
+            val nextCnt = s.cnt + if (s.i < s.j) 2 else 1
+            list.add(State(s.i, s.j, nextCnt, m))
+            recur(chars, State(s.i - 1, s.j + 1, nextCnt, m), list, visited)
+        }
+        recur(chars, State(s.i - 1, s.j, s.cnt, s.mask), list, visited)
+        recur(chars, State(s.i, s.j + 1, s.cnt, s.mask), list, visited)
+    }
+
+    private class State(var i: Int, var j: Int, var cnt: Int, var mask: Int) {
+        override fun equals(other: Any?): Boolean {
+            if (other == null || other.javaClass != this.javaClass) {
+                return false
+            }
+            val s = other as State
+            return i == s.i && j == s.j && mask == s.mask
+        }
+
+        override fun hashCode(): Int {
+            return (i * 31 + j) * 31 + mask
+        }
+    }
+}
+```