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:

Pi Code Challenge

PAST CHALLENGES

Year of the Rabbit

Carol of the Code

Game of Codes

National Coding Week 2022

Jurassic Code

Fury Road

Bug Wars: The Last Hope

Muad'Dib's

Year of the Tiger

Pair a Coder

Code Alone

Gamer's

Spooktober

National Coding Week

The Coder of Rivia

Fast & Curious

The Fellowship of the Code

May the 4th

The Great Code Off 2021

The Doge 2021

The Matrix 2021

The OLX Group challenge

Silver 2020

Palladium 2020

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

There are N towers of stones, numbered from 0 to N−1. The K-th tower contains A[K] stones. In one turn, you can move a single stone from tower K to one of towers K−2, K−1, K+1 or K+2. You can move a stone only to existing towers. For example, from tower 0 you can move a stone only to tower 1 or 2, and from tower 1 you can move a stone only to towers 0, 2 and 3.

What is the minimum number of turns needed to rearrange the stones such that on the K-th tower there will be B[K] stones?

Write a function

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

that, given two arrays A and B of N integers each, representing the initial and final arrangements of the stones, returns the minimum number of turns needed to rearrange the stones. Since the answer can be very large, provide it modulo 10^{9} + 7 (1,000,000,007). If rearrangement is impossible, your function should return −1.

**Examples**

1. Given A = [1, 1, 2, 4, 3], B = [2, 2, 2, 3, 2], your function should return 3. You can move one stone from tower 3 to tower 1 using one turn and one from tower 4 to tower 0 using two turns (4 → 2 → 0).

2. Given A = [0, 0, 2, 1, 8, 8, 2, 0], B = [8, 5, 2, 4, 0, 0, 0, 2], your function should return 31. One possible sequence of moves is as follows:

- move 8 stones from tower 4 to 0 (16 turns),
- move 8 stones from tower 5 to 3 (8 turns),
- move 5 stones from tower 3 to 1 (5 turns),
- move 2 stones from tower 6 to 7 (2 turns).

3. Given A = [10^{9}, 10^{9}, 10^{9}, 0, 0, 0], B = [0, 0, 0, 10^{9}, 10^{9}, 10^{9}], your function should return 999999972. Possible sequence of moves:

- move all stones from tower 0 to 5 (3*10
^{9}turns),- move all stones from tower 1 to 3 (10
^{9}turns),- move all stones from tower 2 to 4 (10
^{9}turns).

The total number of turns is 5*10^{9}, so the answer is 5*10^{9} mod (10^{9}+7) = 999999972.

4. Given A = [2] and B = [1] your function should return −1.

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

- N is an integer within the range [1..100,000];
- arrays A and B have the same length N;
- each element of arrays A and B is an integer within the range [0..1,000,000,000].

Copyright 2009–2024 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.