Tasks Details
elementary
1. DbSum
Calculate sum of elements.
Task Score
100%
Correctness
100%
Performance
Not assessed

Given a table elements with the following structure:

create table elements ( v integer not null )

write an SQL query that returns the sum of the numbers in column v.

For example, given:

v --- 2 10 20 10

your query should return 42.

Copyright 2009–2024 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.
Solution
Programming language used SQL (PostgreSQL)
Total time used 2 minutes
Effective time used 2 minutes
Task timeline
easy
Find and correct bugs in a function that finds a value that occurs in more than half of the elements of an array.
Task Score
100%
Correctness
100%
Performance
Not assessed

A non-empty array A consisting of N integers and sorted in a non-decreasing order (i.e. A[0] ≤ A[1] ≤ ... ≤ A[N−1]) is given. The leader of this array is the value that occurs in more than half of the elements of A.

You are given an implementation of a function:

class Solution { public int solution(int[] A); }

that, given a non-empty array A consisting of N integers, sorted in a non-decreasing order, returns the leader of array A. The function should return −1 if array A does not contain a leader.

For example, given array A consisting of ten elements such that:

A[0] = 2 A[1] = 2 A[2] = 2 A[3] = 2 A[4] = 2 A[5] = 3 A[6] = 4 A[7] = 4 A[8] = 4 A[9] = 6

the function should return −1, because the value that occurs most frequently in the array, 2, occurs five times, and 5 is not more than half of 10.

Given array A consisting of five elements such that:

A[0] = 1 A[1] = 1 A[2] = 1 A[3] = 1 A[4] = 50

the function should return 1.

The attached code is still incorrect for some inputs. Despite the error(s), the code may produce a correct answer for the example test cases. The goal of the exercise is to find and fix the bug(s) in the implementation. You can modify at most three lines.

Assume that:

  • N is an integer within the range [1..100,000];
  • each element of array A is an integer within the range [0..2,147,483,647];
  • array A is sorted in non-decreasing order.

In your solution, focus on correctness. The performance of your solution will not be the focus of the assessment.

Copyright 2009–2024 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.
Solution
Programming language used Java 8
Total time used 1 minutes
Effective time used 1 minutes
Task timeline
medium
Find minimum distance between values in array.
Task Score
60%
Correctness
100%
Performance
0%

Integer V lies strictly between integers U and W if U < V < W or if U > V > W.

A non-empty array A consisting of N integers is given. A pair of indices (P, Q), where 0 ≤ P < Q < N, is said to have adjacent values if no value in the array lies strictly between values A[P] and A[Q].

For example, in array A such that:

A[0] = 0 A[1] = 3 A[2] = 3 A[3] = 7 A[4] = 5 A[5] = 3 A[6] = 11 A[7] = 1

the following pairs of indices have adjacent values:

(0, 7), (1, 2), (1, 4), (1, 5), (1, 7), (2, 4), (2, 5), (2, 7), (3, 4), (3, 6), (4, 5), (5, 7).

For example, indices 4 and 5 have adjacent values because there is no value in array A that lies strictly between A[4] = 5 and A[5] = 3; the only such value could be the number 4, and it is not present in the array.

Given two indices P and Q, their distance is defined as abs(A[P] − A[Q]), where abs(X) = X for X ≥ 0, and abs(X) = −X for X < 0. For example, the distance between indices 4 and 5 is 2 because (A[4] − A[5]) = (5 − 3) = 2.

Write a function:

def solution(A)

that, given a non-empty array A consisting of N integers, returns the minimum distance between indices of this array that have adjacent values. The function should return −1 if the minimum distance is greater than 100,000,000. The function should return −2 if no adjacent indices exist.

For example, given array A such that:

A[0] = 0 A[1] = 3 A[2] = 3 A[3] = 7 A[4] = 5 A[5] = 3 A[6] = 11 A[7] = 1

the function should return 0 because:

  • indices 1 and 2 are adjacent, because the array does not contain any value that lies strictly between A[1] = 3 and A[2] = 3;
  • the distance between these indices is (A[1] − A[2]) = (3 − 3) = 0;
  • no other pair of adjacent indices that has smaller distance exists.

Write an efficient algorithm for the following assumptions:

  • N is an integer within the range [1..40,000];
  • each element of array A is an integer within the range [−2,147,483,648..2,147,483,647].
Copyright 2009–2024 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.
Solution
Programming language used Python
Total time used 3 minutes
Effective time used 3 minutes
Task timeline