Question

2118. Build the Equation

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Description

Table: Terms

+-------------+------+
| Column Name | Type |
+-------------+------+
| power     | int  |
| factor    | int  |
+-------------+------+
power is the column with unique values for this table.
Each row of this table contains information about one term of the equation.
power is an integer in the range [0, 100].
factor is an integer in the range [-100, 100] and cannot be zero.

 

You have a very powerful program that can solve any equation of one variable in the world. The equation passed to the program must be formatted as follows:

• The left-hand side (LHS) should contain all the terms.
• The right-hand side (RHS) should be zero.
• Each term of the LHS should follow the format "<sign><fact>X^<pow>" where:
  • <sign> is either "+" or "-".
  • <fact> is the absolute value of the factor.
  • <pow> is the value of the power.
• If the power is 1, do not add "^<pow>".
  • For example, if power = 1 and factor = 3, the term will be "+3X".
• If the power is 0, add neither "X" nor "^<pow>".
  • For example, if power = 0 and factor = -3, the term will be "-3".
• The powers in the LHS should be sorted in descending order.

Write a solution to build the equation.

The result format is in the following example.

 

Example 1:

Input: 
Terms table:
+-------+--------+
| power | factor |
+-------+--------+
| 2   | 1    |
| 1   | -4   |
| 0   | 2    |
+-------+--------+
Output: 
+--------------+
| equation   |
+--------------+
| +1X^2-4X+2=0 |
+--------------+

Example 2:

Input: 
Terms table:
+-------+--------+
| power | factor |
+-------+--------+
| 4   | -4   |
| 2   | 1    |
| 1   | -1   |
+-------+--------+
Output: 
+-----------------+
| equation    |
+-----------------+
| -4X^4+1X^2-1X=0 |
+-----------------+

 

Follow up: What will be changed in your solution if the power is not a primary key but each power should be unique in the answer?

Solutions

Solution 1

# Write your MySQL query statement below
WITH
  T AS (
    SELECT
      power,
      CASE power
        WHEN 0 THEN IF(factor > 0, CONCAT('+', factor), factor)
        WHEN 1 THEN CONCAT(
          IF(factor > 0, CONCAT('+', factor), factor),
          'X'
        )
        ELSE CONCAT(
          IF(factor > 0, CONCAT('+', factor), factor),
          'X^',
          power
        )
      END AS it
    FROM Terms
  )
SELECT
  CONCAT(GROUP_CONCAT(it ORDER BY power DESC SEPARATOR ""), '=0') AS equation
FROM T;