update

LICENSE.md

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2018 https://github.com/kamyu104/LeetCode-Solution
+Copyright (c) 2018 https://github.com/kamyu104/LeetCode-Solutions
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

MySQL/average-salary-departments-vs-company.sql

@@ -0,0 +1,24 @@
+# Time:  O(nlogn)
+# Space: O(n)
+
+SELECT department_salary.pay_month, department_id,
+CASE
+  WHEN department_avg < company_avg THEN 'lower'
+  WHEN department_avg > company_avg THEN 'higher'
+  ELSE 'same'
+END AS comparison
+FROM
+(
+  SELECT department_id, AVG(amount) AS department_avg, date_format(pay_date, '%Y-%m') AS pay_month
+  FROM salary JOIN employee ON salary.employee_id = employee.employee_id
+  GROUP BY department_id, pay_month
+) AS department_salary
+JOIN
+(
+  SELECT AVG(amount) AS company_avg,  date_format(pay_date, '%Y-%m') AS pay_month
+  FROM salary
+  GROUP BY date_format(pay_date, '%Y-%m')
+) AS company_salary
+ON department_salary.pay_month = company_salary.pay_month
+;
+

MySQL/big-countries.sql

@@ -0,0 +1,7 @@
+# Time:  O(n)
+# Space: O(1)
+
+SELECT name, population, area
+FROM World
+WHERE area > 3000000 OR population > 25000000;
+

MySQL/biggest-single-number.sql

@@ -0,0 +1,20 @@
+# Time:  O(n)
+# Space: O(n)
+
+SELECT
+IFNULL(
+    (SELECT
+        MAX(num)
+    FROM
+        (SELECT
+            num
+        FROM
+            number
+        GROUP BY num
+        HAVING COUNT(num) = 1
+        ORDER BY NULL) AS t
+    )
+    , NULL
+) AS num
+;
+

MySQL/classes-more-than-5-students.sql

@@ -0,0 +1,9 @@
+# Time:  O(n)
+# Space: O(n)
+
+SELECT class
+FROM courses
+GROUP BY class
+HAVING COUNT(DISTINCT student) >= 5
+ORDER BY NULL;
+

MySQL/combine-two-tables.sql

@@ -0,0 +1,6 @@
+# Time:  O(n), n is size of Person Table
+# Space: O(n)
+
+SELECT FirstName, LastName, City, State FROM Person LEFT JOIN Address
+       ON Person.PersonId=Address.PersonId
+

MySQL/consecutive-available-seats.sql

@@ -0,0 +1,10 @@
+# Time:  O(nlogn)
+# Space: O(n)
+
+SELECT DISTINCT c1.seat_id
+FROM cinema c1 JOIN cinema c2
+  ON ((c1.seat_id = c2.seat_id - 1) OR (c1.seat_id = c2.seat_id + 1))
+  AND c1.free = true AND c2.free = true
+ORDER BY c1.seat_id
+;
+

MySQL/consecutive-numbers.sql

@@ -0,0 +1,17 @@
+# Time:  O(n)
+# Space: O(n)
+
+SELECT DISTINCT(Num) AS ConsecutiveNums
+FROM (
+    SELECT
+    Num,
+    @counter := IF(@prev = Num, @counter + 1, 1) AS how_many_cnt_in_a_row,
+    @prev := Num
+    FROM Logs y, (SELECT @counter:=1, @prev:=NULL) vars
+) sq
+WHERE how_many_cnt_in_a_row >= 3
+
+SELECT DISTINCT l1.Num  as ConsecutiveNums
+FROM Logs l1, Logs l2, Logs l3  
+WHERE l1.Id + 1 = l2.Id AND l2.Id + 1 = l3.Id AND l1.Num = l2.Num AND l2.Num = l3.Num 
+

MySQL/count-student-number-in-department.sql

@@ -0,0 +1,13 @@
+# Time:  O(s+dlogd)
+# Space: O(d+s)
+
+SELECT
+    dept_name, COUNT(student_id) AS student_number
+FROM
+    department
+        LEFT JOIN
+    student ON department.dept_id = student.dept_id
+GROUP BY department.dept_name
+ORDER BY student_number DESC , department.dept_name
+;
+

MySQL/customer-placing-the-largest-number-of-orders.sql

@@ -0,0 +1,20 @@
+# Time:  O(n)
+# Space: O(n)
+
+SELECT customer_number
+FROM orders
+GROUP BY customer_number
+HAVING COUNT(order_number) = 
+     (SELECT MAX(*)
+     FROM
+        (SELECT COUNT(*) AS cnt
+        FROM
+            orders
+        GROUP BY customer_number
+        ORDER BY NULL
+        ) AS cnt_tbl
+     )
+ORDER BY NULL
+LIMIT 1
+;
+

MySQL/customers-who-never-order.sql

@@ -0,0 +1,7 @@
+# Time:  O(n^2)
+# Space: O(1)
+
+SELECT Name AS Customers FROM Customers WHERE Id NOT IN (SELECT CustomerId FROM Orders)
+
+SELECT Customers.Name AS Customers FROM (Customers LEFT JOIN Orders ON Customers.Id = Orders.CustomerId) WHERE Orders.CustomerId IS NULL
+

MySQL/delete-duplicate-emails.sql

@@ -0,0 +1,7 @@
+# Time:  O(n^2)
+# Space: O(n)
+
+DELETE p1
+FROM Person p1, Person p2
+WHERE p1.Email = p2.Email AND p1.Id > p2.Id
+

MySQL/department-highest-salary.sql

@@ -0,0 +1,14 @@
+# Time:  O(n^2)
+# Space: O(n)
+
+SELECT d.Department AS Department, e.Name AS Employee, d.Salary AS Salary
+FROM (SELECT Department.Id AS DepartmentId, Department.Name AS Department, emp.Salary AS Salary
+        FROM Department JOIN (SELECT DepartmentId, MAX(Salary) AS Salary FROM Employee GROUP BY DepartmentId) emp
+        ON Department.Id = emp.DepartmentId) d 
+      JOIN Employee e 
+      ON e.DepartmentId = d.DepartmentId and e.Salary = d.Salary
+
+SELECT Department.Name AS Department, Employee.Name AS Employee, Employee.Salary AS Salary
+FROM Department JOIN Employee ON Employee.DepartmentId = Department.Id
+WHERE Employee.Salary IN (SELECT MAX(e.Salary) FROM Employee e WHERE e.DepartmentId = Employee.DepartmentId)
+

MySQL/department-top-three-salaries.sql

@@ -0,0 +1,9 @@
+# Time:  O(n^2)
+# Space: O(n)
+
+SELECT D.Name AS Department, E.Name AS Employee, E.Salary AS Salary 
+FROM Employee E INNER JOIN Department D ON E.DepartmentId = D.Id 
+WHERE (SELECT COUNT(DISTINCT(Salary)) FROM Employee 
+       WHERE DepartmentId = E.DepartmentId AND Salary > E.Salary) < 3
+ORDER by E.DepartmentId, E.Salary DESC;
+

MySQL/duplicate-emails.sql

@@ -0,0 +1,5 @@
+# Time:  O(n^2)
+# Space: O(n)
+
+SELECT Email FROM Person GROUP BY Email HAVING COUNT(*) > 1
+

MySQL/employee-bonus.sql

@@ -0,0 +1,13 @@
+# Time:  O(n) if hash join, O(nlogn) if merge join
+# Space: O(n)
+
+SELECT
+    Employee.name, Bonus.bonus
+FROM
+    Employee
+        LEFT JOIN
+    Bonus ON Employee.empid = Bonus.empid
+WHERE
+    Bonus.bonus < 1000 OR Bonus.bonus IS NULL
+;
+

MySQL/employees-earning-more-than-their-managers.sql

@@ -0,0 +1,13 @@
+# Time: O(n^2)
+# Space: O(1)
+
+SELECT e.Name AS Employee  FROM Employee e LEFT JOIN Employee b
+       ON e.ManagerId=b.Id
+       WHERE e.Salary > b.Salary
+
+SELECT Name AS Employee 
+    FROM Employee e 
+    WHERE e.ManagerId IS NOT NULL AND e.Salary > (SELECT Salary 
+                          FROM Employee 
+                          WHERE e.ManagerId = Id)
+

MySQL/exchange-seats.sql

@@ -0,0 +1,11 @@
+# Time:  O(nlogn)
+# Space: O(n)
+
+SELECT
+    s1.id, COALESCE(s2.student, s1.student) AS student
+FROM
+    seat s1
+        LEFT JOIN
+    seat s2 ON ((s1.id + 1) ^ 1) - 1 = s2.id
+ORDER BY s1.id;
+

MySQL/find-cumulative-salary-of-an-employee.sql

@@ -0,0 +1,23 @@
+# Time:  O(n^2)
+# Space: O(n)
+
+SELECT EA.Id, 
+       EA.Month, 
+       SUM(EB.salary) AS Salary 
+FROM   (SELECT E1.* 
+        FROM   employee E1 
+               LEFT JOIN (SELECT id, 
+                                 MAX(month) AS month 
+                          FROM   employee 
+                          GROUP  BY id) E2 
+                      ON E1.id = E2.id 
+        WHERE  E1.month < E2.month) EA 
+       LEFT JOIN employee EB 
+              ON EA.id = EB.id 
+WHERE  EA.month - 2 <= EB.month
+       AND EB.month <= EA.month
+GROUP  BY EA.id, 
+          EA.month 
+ORDER  BY EA.id, 
+          month DESC 
+

MySQL/find-customer-referee.sql

@@ -0,0 +1,7 @@
+# Time:  O(n)
+# Space: O(1)
+
+SELECT name
+FROM customer 
+WHERE referee_id is NULL OR referee_id != 2;
+

MySQL/find-median-given-frequency-of-numbers.sql

@@ -0,0 +1,16 @@
+# Time:  O(nlogn)
+# Space: O(n)
+
+SELECT AVG(n.Number) AS median 
+FROM Numbers n LEFT JOIN
+(
+SELECT Number, @prev := @count AS prevNumber, (@count := @count + Frequency) AS countNumber
+FROM Numbers, 
+(SELECT @count := 0, @prev := 0, @total := (SELECT SUM(Frequency) FROM Numbers)) temp ORDER BY Number
+) n2
+ON n.Number = n2.Number
+WHERE 
+(prevNumber < floor((@total+1)/2) AND countNumber >= floor((@total+1)/2))
+OR
+(prevNumber < floor((@total+2)/2) AND countNumber >= floor((@total+2)/2))
+

MySQL/friend-requests-i-overall-acceptance-rate.sql

@@ -0,0 +1,12 @@
+# Time:  O(rlogr + aloga)
+# Space: O(r + a)
+
+SELECT
+ROUND(
+    IFNULL(
+    (SELECT COUNT(*) FROM (SELECT DISTINCT requester_id, accepter_id FROM request_accepted) AS r)
+    /
+    (SELECT COUNT(*) FROM (SELECT DISTINCT sender_id, send_to_id FROM friend_request) AS a),
+    0)
+, 2) AS accept_rate;
+

MySQL/friend-requests-ii-who-has-the-most-friends.sql

@@ -0,0 +1,15 @@
+# Time:  O(nlogn)
+# Space: O(n)
+
+SELECT ids as id, COUNT(*) AS num
+   FROM
+   (
+        SELECT requester_id AS ids FROM request_accepted
+        UNION ALL
+        SELECT accepter_id FROM request_accepted
+    ) AS tmp
+GROUP BY ids
+ORDER BY num DESC
+LIMIT 1
+;
+

MySQL/get-highest-answer-rate-question.sql

@@ -0,0 +1,11 @@
+# Time:  O(nlogn)
+# Space: O(n)
+
+SELECT 
+    question_id AS 'survey_log'
+FROM
+    survey_log
+GROUP BY question_id
+ORDER BY COUNT(answer_id) / COUNT(IF(action = 'show', 1, 0)) DESC
+LIMIT 1;
+

MySQL/human-traffic-of-stadium.sql

@@ -0,0 +1,17 @@
+# Time:  O(n^3)
+# Space: O(n^3)
+
+SELECT DISTINCT s1.*
+FROM stadium AS s1, stadium AS s2, stadium AS s3
+WHERE s1.people >= 100 AND s2.people >= 100 AND s3.people >= 100
+AND
+(
+    (s2.id = s1.id + 1 AND s3.id = s2.id + 1 AND s3.id = s1.id + 2) -- s1, s2, s3
+    OR
+    (s1.id = s2.id + 1 AND s3.id = s1.id + 1 AND s3.id = s2.id + 2) -- s2, s1, s3
+    OR
+    (s3.id = s2.id + 1 AND s1.id = s3.id + 1 AND s1.id = s2.id + 2) -- s2, s3, s1
+)
+ORDER BY s1.id
+;
+

MySQL/investments-in-2016.sql

@@ -0,0 +1,30 @@
+# Time:  O(n^2)
+# Space: O(n)
+
+SELECT
+    SUM(insurance.TIV_2016) AS TIV_2016
+FROM
+    insurance
+WHERE
+    insurance.TIV_2015 IN
+    (
+      SELECT
+        TIV_2015
+      FROM
+        insurance
+      GROUP BY TIV_2015
+      HAVING COUNT(*) > 1
+      ORDER BY NULL
+    )
+    AND CONCAT(LAT, LON) IN
+    (
+      SELECT
+        CONCAT(LAT, LON)
+      FROM
+        insurance
+      GROUP BY LAT , LON
+      HAVING COUNT(*) = 1
+      ORDER BY NULL
+    )
+;
+

MySQL/managers-with-at-least-5-direct-reports.sql

@@ -0,0 +1,17 @@
+# Time:  O(n)
+# Space: O(n)
+
+SELECT
+    Name
+FROM
+    Employee AS t1 INNER JOIN
+    (SELECT
+        ManagerId
+    FROM
+        Employee
+    GROUP BY ManagerId
+    HAVING COUNT(ManagerId) >= 5
+    ORDER BY NULL) AS t2
+    ON t1.Id = t2.ManagerId
+;
+