Added tasks 1934, 1978, 2356, 2552, 2553

Author: ThanhNIT

src/main/java/g1901_2000/s1934_confirmation_rate/readme.md

@@ -0,0 +1,86 @@
+1934\. Confirmation Rate
+
+Medium
+
+SQL Schema
+
+Table: `Signups`
+
+    +----------------+----------+
+    | Column Name    | Type     |
+    +----------------+----------+
+    | user_id        | int      |
+    | time_stamp     | datetime |
+    +----------------+----------+
+    user_id is the primary key for this table.
+    Each row contains information about the signup time for the user with ID user_id.
+
+Table: `Confirmations`
+
+    +----------------+----------+
+    | Column Name    | Type     |
+    +----------------+----------+
+    | user_id        | int      |
+    | time_stamp     | datetime |
+    | action         | ENUM     |
+    +----------------+----------+
+    (user_id, time_stamp) is the primary key for this table.
+    user_id is a foreign key with a reference to the Signups table.
+    action is an ENUM of the type ('confirmed', 'timeout')
+    Each row of this table indicates that the user with ID user_id requested a confirmation message at time_stamp and that confirmation message was either confirmed ('confirmed') or expired without confirming ('timeout'). 
+
+The **confirmation rate** of a user is the number of `'confirmed'` messages divided by the total number of requested confirmation messages. The confirmation rate of a user that did not request any confirmation messages is `0`. Round the confirmation rate to **two decimal** places.
+
+Write an SQL query to find the **confirmation rate** of each user.
+
+Return the result table in **any order**.
+
+The query result format is in the following example.
+
+**Example 1:**
+
+**Input:**
+
+    Signups table:
+    +---------+---------------------+
+    | user_id | time_stamp          |
+    +---------+---------------------+
+    | 3       | 2020-03-21 10:16:13 |
+    | 7       | 2020-01-04 13:57:59 |
+    | 2       | 2020-07-29 23:09:44 |
+    | 6       | 2020-12-09 10:39:37 |
+    +---------+---------------------+
+
+    Confirmations table:
+    +---------+---------------------+-----------+
+    | user_id | time_stamp          | action    |
+    +---------+---------------------+-----------+
+    | 3       | 2021-01-06 03:30:46 | timeout   |
+    | 3       | 2021-07-14 14:00:00 | timeout   |
+    | 7       | 2021-06-12 11:57:29 | confirmed |
+    | 7       | 2021-06-13 12:58:28 | confirmed |
+    | 7       | 2021-06-14 13:59:27 | confirmed |
+    | 2       | 2021-01-22 00:00:00 | confirmed |
+    | 2       | 2021-02-28 23:59:59 | timeout   |
+    +---------+---------------------+-----------+
+
+**Output:**
+
+    +---------+-------------------+
+    | user_id | confirmation_rate |
+    +---------+-------------------+
+    | 6       | 0.00              |
+    | 3       | 0.00              |
+    | 7       | 1.00              |
+    | 2       | 0.50              |
+    +---------+-------------------+
+
+**Explanation:**
+
+User 6 did not request any confirmation messages. The confirmation rate is 0.
+
+User 3 made 2 requests and both timed out. The confirmation rate is 0.
+
+User 7 made 3 requests and all were confirmed. The confirmation rate is 1.
+
+User 2 made 2 requests where one was confirmed and the other timed out. The confirmation rate is 1 / 2 = 0.5.

src/main/java/g1901_2000/s1934_confirmation_rate/script.sql

@@ -0,0 +1,21 @@
+# Write your MySQL query statement below
+# #Medium #Database #2023_08_17_Time_1432_ms_(68.14%)_Space_0B_(100.00%)
+WITH base_table AS (
+    SELECT
+        t.user_id,
+        ROUND(t.total_confirmed / t.total_messages,2) AS confirmation_rate
+    FROM (
+        SELECT
+            user_id ,
+            SUM(CASE WHEN action='confirmed' THEN 1 ELSE 0 END) AS total_confirmed,
+            COUNT(*) AS total_messages
+        FROM confirmations
+        GROUP BY 1
+    ) t
+)
+SELECT
+    s.user_id,
+    COALESCE(bt.confirmation_rate,0) AS confirmation_rate
+FROM signups s
+LEFT JOIN base_table bt
+ON s.user_id = bt.user_id

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

@@ -0,0 +1,55 @@
+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. 

src/main/java/g1901_2000/s1978_employees_whose_manager_left_the_company/script.sql

@@ -0,0 +1,4 @@
+# Write your MySQL query statement below
+# #Easy #Database #2023_08_17_Time_719_ms_(64.69%)_Space_0B_(100.00%)
+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/java/g2301_2400/s2356_number_of_unique_subjects_taught_by_each_teacher/readme.md

@@ -0,0 +1,68 @@
+2356\. Number of Unique Subjects Taught by Each Teacher
+
+Easy
+
+SQL Schema
+
+Table: `Teacher`
+
+    +-------------+------+
+    | Column Name | Type |
+    +-------------+------+
+    | teacher_id  | int  |
+    | subject_id  | int  |
+    | dept_id     | int  |
+    +-------------+------+
+    (subject_id, dept_id) is the primary key for this table.
+    Each row in this table indicates that the teacher with teacher_id teaches the subject subject_id in the department dept_id. 
+
+Write an SQL query to report the number of unique subjects each teacher teaches in the university.
+
+Return the result table in **any order**.
+
+The query result format is shown in the following example.
+
+**Example 1:**
+
+**Input:**
+
+Teacher table:
+
+    +------------+------------+---------+
+    | teacher_id | subject_id | dept_id |
+    +------------+------------+---------+
+    | 1          | 2          | 3       |
+    | 1          | 2          | 4       |
+    | 1          | 3          | 3       |
+    | 2          | 1          | 1       |
+    | 2          | 2          | 1       |
+    | 2          | 3          | 1       |
+    | 2          | 4          | 1       |
+    +------------+------------+---------+
+
+**Output:**
+
+    +------------+-----+
+    | teacher_id | cnt |
+    +------------+-----+
+    | 1          | 2   |
+    | 2          | 4   |
+    +------------+-----+
+
+**Explanation:**
+
+Teacher 1:
+
+- They teach subject 2 in departments 3 and 4.
+
+- They teach subject 3 in department 3.
+
+Teacher 2:
+
+- They teach subject 1 in department 1.
+
+- They teach subject 2 in department 1.
+
+- They teach subject 3 in department 1.
+
+- They teach subject 4 in department 1. 

src/main/java/g2301_2400/s2356_number_of_unique_subjects_taught_by_each_teacher/script.sql

@@ -0,0 +1,5 @@
+# Write your MySQL query statement below
+# #Easy #Database #2023_08_17_Time_964_ms_(79.65%)_Space_0B_(100.00%)
+select teacher_id, count(distinct subject_id) as "cnt"
+from Teacher
+group by teacher_id

src/main/java/g2501_2600/s2552_count_increasing_quadruplets/Solution.java

@@ -0,0 +1,27 @@
+package g2501_2600.s2552_count_increasing_quadruplets;
+
+// #Hard #Array #Dynamic_Programming #Prefix_Sum #Enumeration #Binary_Indexed_Tree
+// #2023_08_18_Time_48_ms_(97.29%)_Space_43_MB_(93.41%)
+
+import java.util.Arrays;
+
+class Solution {
+    public long countQuadruplets(int[] nums) {
+        int n = nums.length;
+        long[] dp = new long[n];
+        Arrays.fill(dp, 0);
+        long ret = 0;
+        for (int i = 1; i < n; i++) {
+            int choice = 0;
+            for (int j = 0; j < i; j++) {
+                if (nums[i] > nums[j]) {
+                    choice++;
+                    ret += dp[j];
+                } else if (nums[i] < nums[j]) {
+                    dp[j] += choice;
+                }
+            }
+        }
+        return ret;
+    }
+}

src/main/java/g2501_2600/s2552_count_increasing_quadruplets/readme.md

@@ -0,0 +1,38 @@
+2552\. Count Increasing Quadruplets
+
+Hard
+
+Given a **0-indexed** integer array `nums` of size `n` containing all numbers from `1` to `n`, return _the number of increasing quadruplets_.
+
+A quadruplet `(i, j, k, l)` is increasing if:
+
+*   `0 <= i < j < k < l < n`, and
+*   `nums[i] < nums[k] < nums[j] < nums[l]`.
+
+**Example 1:**
+
+**Input:** nums = [1,3,2,4,5]
+
+**Output:** 2
+
+**Explanation:**
+
+- When i = 0, j = 1, k = 2, and l = 3, nums[i] < nums[k] < nums[j] < nums[l].
+
+- When i = 0, j = 1, k = 2, and l = 4, nums[i] < nums[k] < nums[j] < nums[l]. There are no other quadruplets, so we return 2. 
+
+**Example 2:**
+
+**Input:** nums = [1,2,3,4]
+
+**Output:** 0
+
+**Explanation:**
+
+There exists only one quadruplet with i = 0, j = 1, k = 2, l = 3, but since nums[j] < nums[k], we return 0. 
+
+**Constraints:**
+
+*   `4 <= nums.length <= 4000`
+*   `1 <= nums[i] <= nums.length`
+*   All the integers of `nums` are **unique**. `nums` is a permutation.

src/main/java/g2501_2600/s2553_separate_the_digits_in_an_array/Solution.java

@@ -0,0 +1,18 @@
+package g2501_2600.s2553_separate_the_digits_in_an_array;
+
+// #Easy #Array #Simulation #2023_08_18_Time_3_ms_(92.00%)_Space_43.7_MB_(93.70%)
+
+class Solution {
+    public int[] separateDigits(int[] nums) {
+        StringBuilder str = new StringBuilder();
+        for (int num : nums) {
+            str.append(num);
+        }
+        int[] ar = new int[str.length()];
+        String s = str.toString();
+        for (int i = 0; i < s.length(); i++) {
+            ar[i] = s.charAt(i) - '0';
+        }
+        return ar;
+    }
+}

src/main/java/g2501_2600/s2553_separate_the_digits_in_an_array/readme.md

@@ -0,0 +1,42 @@
+2553\. Separate the Digits in an Array
+
+Easy
+
+Given an array of positive integers `nums`, return _an array_ `answer` _that consists of the digits of each integer in_ `nums` _after separating them in **the same order** they appear in_ `nums`.
+
+To separate the digits of an integer is to get all the digits it has in the same order.
+
+*   For example, for the integer `10921`, the separation of its digits is `[1,0,9,2,1]`.
+
+**Example 1:**
+
+**Input:** nums = [13,25,83,77]
+
+**Output:** [1,3,2,5,8,3,7,7]
+
+**Explanation:**
+
+- The separation of 13 is [1,3].
+
+- The separation of 25 is [2,5].
+
+- The separation of 83 is [8,3].
+
+- The separation of 77 is [7,7].
+
+answer = [1,3,2,5,8,3,7,7]. Note that answer contains the separations in the same order.
+
+**Example 2:**
+
+**Input:** nums = [7,1,3,9]
+
+**Output:** [7,1,3,9]
+
+**Explanation:**
+
+The separation of each integer in nums is itself. answer = [7,1,3,9].
+
+**Constraints:**
+
+*   `1 <= nums.length <= 1000`
+*   <code>1 <= nums[i] <= 10<sup>5</sup></code>