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# Choose atleast two elements from array such that their GCD is 1 and cost is minimum

• Difficulty Level : Medium
• Last Updated : 02 Jun, 2021

Given two integer arrays arr[] and cost[] where cost[i] is the cost of choosing arr[i]. The task is to choose a subset with at least two elements such that the GCD of all the elements from the subset is 1 and the cost of choosing those elements is as minimum as possible then print the minimum cost.
Examples:

Input: arr[] = {5, 10, 12, 1}, cost[] = {2, 1, 2, 6}
Output:
{5, 12} is the required subset with cost = 2 + 2 = 4
Input: arr[] = {50, 100, 150, 200, 300}, cost[] = {2, 3, 4, 5, 6}
Output: -1
No subset possible with gcd = 1

Approach: Add GCD of any two elements to a map, now for every element arr[i] calculate its gcd with all the gcd values found so far (saved in the map) and update map[gcd] = min(map[gcd], map[gcd] + cost[i]). If in the end, map doesn’t contain any entry for gcd = 1 then print -1 else print the stored minimum cost.
Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `// Function to return the minimum cost required``int` `getMinCost(``int` `arr[], ``int` `n, ``int` `cost[])``{` `    ``// Map to store pair where``    ``// cost is the cost to get the current gcd``    ``map<``int``, ``int``> mp;``    ``mp.clear();``    ``mp = 0;` `    ``for` `(``int` `i = 0; i < n; i++) {``        ``for` `(``auto` `it : mp) {``            ``int` `gcd = __gcd(arr[i], it.first);` `            ``// If current gcd value already exists in map``            ``if` `(mp.count(gcd) == 1)` `                ``// Update the minimum cost``                ``// to get the current gcd``                ``mp[gcd] = min(mp[gcd], it.second + cost[i]);` `            ``else``                ``mp[gcd] = it.second + cost[i];``        ``}``    ``}` `    ``// If there can be no sub-set such that``    ``// the gcd of all the elements is 1``    ``if` `(mp == 0)``        ``return` `-1;``    ``else``        ``return` `mp;``}` `// Driver code``int` `main()``{``    ``int` `arr[] = { 5, 10, 12, 1 };``    ``int` `cost[] = { 2, 1, 2, 6 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);` `    ``cout << getMinCost(arr, n, cost);``    ``return` `0;``}`

## Java

 `// Java implementation of the approach` `import` `java.util.*;``import` `java.util.concurrent.ConcurrentHashMap;` `class` `GFG{`` ` `// Function to return the minimum cost required``static` `int` `getMinCost(``int` `arr[], ``int` `n, ``int` `cost[])``{`` ` `    ``// Map to store pair where``    ``// cost is the cost to get the current gcd``    ``Map mp = ``new` `ConcurrentHashMap();``    ``mp.clear();``    ``mp.put(``0``, ``0``);`` ` `    ``for` `(``int` `i = ``0``; i < n; i++) {``        ``for` `(Map.Entry it : mp.entrySet()){``            ``int` `gcd = __gcd(arr[i], it.getKey());`` ` `            ``// If current gcd value already exists in map``            ``if` `(mp.containsKey(gcd))`` ` `                ``// Update the minimum cost``                ``// to get the current gcd``                ``mp.put(gcd, Math.min(mp.get(gcd), it.getValue() + cost[i]));`` ` `            ``else``                ``mp.put(gcd,it.getValue() + cost[i]);``        ``}``    ``}`` ` `    ``// If there can be no sub-set such that``    ``// the gcd of all the elements is 1``    ``if` `(!mp.containsKey(``1``))``        ``return` `-``1``;``    ``else``        ``return` `mp.get(``1``);``}``static` `int` `__gcd(``int` `a, ``int` `b) ``{ ``    ``return` `b == ``0``? a:__gcd(b, a % b);    ``}``// Driver code``public` `static` `void` `main(String[] args)``{``    ``int` `arr[] = { ``5``, ``10``, ``12``, ``1` `};``    ``int` `cost[] = { ``2``, ``1``, ``2``, ``6` `};``    ``int` `n = arr.length;`` ` `    ``System.out.print(getMinCost(arr, n, cost));``}``}` `// This code is contributed by PrinciRaj1992`

## Python3

 `# Python3 implementation of the approach``from` `math ``import` `gcd as __gcd` `# Function to return the minimum cost required``def` `getMinCost(arr, n, cost):` `    ``# Map to store pair where``    ``# cost is the cost to get the current gcd``    ``mp ``=` `dict``()``    ``mp[``0``] ``=` `0` `    ``for` `i ``in` `range``(n):``        ``for` `it ``in` `list``(mp):``            ``gcd ``=` `__gcd(arr[i], it)` `            ``# If current gcd value``            ``# already exists in map``            ``if` `(gcd ``in` `mp):` `                ``# Update the minimum cost``                ``# to get the current gcd``                ``mp[gcd] ``=` `min``(mp[gcd],``                              ``mp[it] ``+` `cost[i])` `            ``else``:``                ``mp[gcd] ``=` `mp[it] ``+` `cost[i]` `    ``# If there can be no sub-set such that``    ``# the gcd of all the elements is 1``    ``if` `(mp[``1``] ``=``=` `0``):``        ``return` `-``1``    ``else``:``        ``return` `mp[``1``]` `# Driver code``arr ``=` `[ ``5``, ``10``, ``12``, ``1``]``cost ``=` `[ ``2``, ``1``, ``2``, ``6``]``n ``=` `len``(arr)` `print``(getMinCost(arr, n, cost))` `# This code is contributed by Mohit Kumar`

## C#

 `// C# implementation of the approach``using` `System;``using` `System.Collections.Generic;``using` `System.Linq;``class` `GFG``{``  ``static` `int` `__gcd(``int` `a, ``int` `b)  ``  ``{  ``    ``return` `b == 0? a:__gcd(b, a % b);     ``  ``}` `  ``// Function to return the minimum cost required``  ``static` `int` `getMinCost(``int``[] arr, ``int` `n, ``int``[] cost)``  ``{` `    ``// Map to store pair where``    ``// cost is the cost to get the current gcd``    ``Dictionary<``int``, ``int``> mp = ``new` `Dictionary<``int``, ``int``>();``    ``mp.Add(0, 0);``    ``for` `(``int` `i = 0; i < n; i++)``    ``{` `      ``foreach` `(``int` `it ``in` `mp.Keys.ToList())``      ``{``        ``int` `gcd = __gcd(arr[i], it);` `        ``// If current gcd value already exists in map``        ``if``(mp.ContainsKey(gcd))``        ``{` `          ``// Update the minimum cost``          ``// to get the current gcd``          ``mp[gcd] = Math.Min(mp[gcd], mp[it] + cost[i]);``        ``}``        ``else``        ``{``          ``mp.Add(gcd, mp[it] + cost[i]);``        ``}``      ``} ``    ``}` `    ``// If there can be no sub-set such that``    ``// the gcd of all the elements is 1``    ``if` `(mp == 0)``    ``{``      ``return` `-1;``    ``}``    ``else``    ``{``      ``return` `mp;``    ``}       ``  ``}` `  ``// Driver code``  ``static` `public` `void` `Main ()``  ``{``    ``int``[] arr = { 5, 10, 12, 1 };``    ``int``[] cost = { 2, 1, 2, 6 };``    ``int` `n = arr.Length;``    ``Console.WriteLine(getMinCost(arr, n, cost));``  ``}``}` `// This code is contributed by avanitrachhadiya2155`

## Javascript

 ``
Output:
`4`

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