Your browser (Unknown 0) is no longer supported. Some parts of the website may not work correctly. Please update your browser.

UPCOMING CHALLENGES:

CURRENT CHALLENGES:

Palladium 2020

PAST CHALLENGES

Rhodium 2019

Ruthenium 2019

Technetium 2019

Molybdenum 2019

Niobium 2019

Zirconium 2019

Yttrium 2019

Strontium 2019

Rubidium 2018

Arsenicum 2018

Krypton 2018

Bromum 2018

Future Mobility

Grand Challenge

Digital Gold

Selenium 2018

Germanium 2018

Gallium 2018

Zinc 2018

Cuprum 2018

Cutting Complexity

Nickel 2018

Cobaltum 2018

Ferrum 2018

Manganum 2017

Chromium 2017

Vanadium 2016

Titanium 2016

Scandium 2016

Calcium 2015

Kalium 2015

Argon 2015

Chlorum 2014

Sulphur 2014

Phosphorus 2014

Silicium 2014

Aluminium 2014

Magnesium 2014

Natrium 2014

Neon 2014

Fluorum 2014

Oxygenium 2014

Nitrogenium 2013

Carbo 2013

Boron 2013

Beryllium 2013

Lithium 2013

Helium 2013

Hydrogenium 2013

Omega 2013

Psi 2012

Chi 2012

Phi 2012

Upsilon 2012

Tau 2012

Sigma 2012

Rho 2012

Pi 2012

Omicron 2012

Xi 2012

Nu 2011

Mu 2011

Lambda 2011

Kappa 2011

Iota 2011

Theta 2011

Eta 2011

Zeta 2011

Epsilon 2011

Delta 2011

Gamma 2011

Beta 2010

Alpha 2010

Given an array A, count the number of different triplets (a, b, c) in which a occurs before b and b occurs before c.

Programming language:

Kate was given a birthday gift of three theater tickets. Now she is browsing the theater program for the next N days. On the program, performances are named by integers. Every day, one performance is staged. Kate wants to choose three days (not necessarily consecutive) to go to the theater.

In how many ways can she use her tickets? Two ways are different if the sequences of watched performances are different. Kate likes the theater, so she may watch one performance more than once. For example, if N = 4 and theater program looks as following: [1, 2, 1, 1], Kate has four possibilities to choose the dates: [**1, 2, 1, **1], [**1, 2, **1,** 1**], [**1, **2,** 1, 1**], and [1, **2, 1, 1**], but they create only three different sequences: (1, 2, 1), (1, 1, 1) and (2, 1, 1). The correct answer for this example is 3. Notice that the order of performances matters, so the first and the last sequences are considered different.

Write a function:

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

that, given an array A consisting of N integers, denoting names of performances for the next N days, returns the number of possible ways to spend the tickets. Since the answer can be very large, provide it modulo 10^{9} + 7 (1,000,000,007).

For example, given A = [1, 2, 1, 1], the function should return 3 as exmplained above.

Given A = [1, 2, 3, 4], the function should return 4. There are four ways to spend tickets: (1, 2, 3), (1, 2, 4), (1, 3, 4) and (2, 3, 4).

Given A = [2, 2, 2, 2], the function should return 1. There is only one way to spend tickets: (2, 2, 2).

Given A = [2, 2, 1, 2, 2], the function should return 4. There are four ways to spend tickets: (1, 2, 2), (2, 1, 2), (2, 2, 1) and (2, 2, 2).

Given A = [1, 2], the function should return 0. Kate cannot use all three tickets in only two days.

Write an ** efficient** algorithm for the following assumptions:

- N is an integer within the range [0..100,000];
- each element of array A is an integer within the range [1..N].

Copyright 2009–2020 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.