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:

Year of the Rabbit

PAST CHALLENGES

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

Place the minimum number of guards needed to prevent prisoners from escaping.

There are N+1 intersections in a prison, connected by N corridors, and one can move between any two intersections using the corridors. Intersections with only one corridor are located near the exits from the prison.

There is a cell block near every intersection. Exactly M cell blocks hold prisoners; others are empty. Due to a malfunction in the locking system, all the cells have been opened. The situation is critical and the governor of the prison needs to know where to position the guards in order to prevent the prisoners from escaping.

You are given a map of the prison in the form of two arrays A, B of length N and an array C of length M:

- For each I (0 ≤ I < N) there is a corridor between intersections A[I] and B[I].
- For each I (0 ≤ I < M) there are prisoners in the cell block near intersection C[I].

A guard can be located at an intersection, but not at an intersections near to a cell block which initially held prisoners. Prisoners from a cell block located near intersection X can escape from the prison if there is a path from X to an intersection located near an exit from the prison and there are no guards at any intersection along this path. The governor would like to know the minimum number of guards he must deploy in the operation.

Write a function:

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

that, given arrays A, B of N integers and array C of M integers, returns the minimum number of guards that can prevent all prisoners from escaping. If there is no way to prevent an escape of some prisoner, the function should return −1.

For example, given the following arrays:

the function should return 4. Four guards can be positioned at the intersections numbered 0, 3, 7 and 8 (another solution would be to position guards at intersections 0, 2, 7 and 8). By positioning three or fewer guards, the governor is unable to prevent some prisoners from escaping.

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

- N is an integer within the range [1..200,000];
- M is an integer within the range [0..
N+1];- each element of arrays A, B and C is an integer within the range [0..N];
- the elements of C are all distinct;
- distance from intersection 0 to any other intersection is not greater than 500.

Copyright 2009–2023 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.