Minimize count of divisions by D to obtain at least K equal array elements - GeeksforGeeks

17 Jul, 2021
Given an array A[ ] of size N and two integers K and D, the task is to calculate the minimum possible number of operations required to obtain at least K equal array elements. Each operation involves replacing an element A[i] by A[i] / D. This operation can be performed any number of times.
Examples: 
Input: N = 5, A[ ] = {1, 2, 3, 4, 5}, K = 3, D = 2 Output: 2 Explanation: Step 1: Replace A[3] by A[3] / D, i.e. (4 / 2) = 2. Hence, the array modifies to {1, 2, 3, 2, 5} Step 2: Replace A[4] by A[4] / D, i.e. (5 / 2) = 2. Hence, the array modifies to {1, 2, 3, 2, 2} Hence, the modified array has K(= 3) equal elements. Hence, the minimum number of operations required is 2.
Input: N = 4, A[ ] = {1, 2, 3, 6}, K = 2, D = 3 Output: 1 Explanation:Replacing A[3] by A[3] / D, i.e. (6 / 3) = 2. Hence, the array modifies to {1, 2, 3, 2}. Hence, the modified array has K(= 2) equal elements. Hence, the minimum number of operations required is 1. 
Naive Approach: The simplest approach to solve the problem is to generate every possible subset of the given array and perform the given operation on all elements of this subset. The number of operations required for each subset will be equal to the size of the subset. For each subset, count the number of equal elements and check if count is equal to K. If so, compare the then count with minimum moves obtained so far and update accordingly. Finally, print the minimum moves.
Time Complexity: O(2N *N) Auxiliary Space: O(N)
Efficient Approach: Follow the steps below to solve the problem: 
Initialize a 2D vector V, in which, size of a row V[i] denotes the number of array elements that have been reduced to A[i] and every element of the row denotes a count of divisions by D performed on an array element to obtain the number i.
Traverse the array. For each element A[i], keep dividing it by D until it reduces to 0.
For each intermediate value of A[i] obtained in the above step, insert the number of divisions required into V[A[i]].
Once, the above steps are completed for the entire array, iterate over the array V[ ].
For each V[i], check if the size of V[i] ≥ K (at most K).
If V[i] ≥ K, it denotes that at least K elements in the array have been reduced to i. Sort V[i] and add the first K values, i.e. the smallest K moves required to make K elements equal in the array.
Compare the sum of K moves with the minimum moves required and update accordingly.
Once the traversal of the array V[] is completed, print the minimum count of moves obtained finally.
Below is the implementation of the above approach:
C++
Java
Python3
C#
// C++ Program to implement// the above approach#include <bits/stdc++.h>using namespace std; // Function to return minimum// number of moves requiredint getMinimumMoves(int n, int k, int d,                    vector<int> a){    int MAX = 100000;     // Stores the number of moves    // required to obtain respective    // values from the given array    vector<int> v[MAX];     // Traverse the array    for (int i = 0; i < n; i++) {        int cnt = 0;         // Insert 0 into V[a[i]] as        // it is the initial state        v[a[i]].push_back(0);         while (a[i] > 0) {            a[i] /= d;            cnt++;             // Insert the moves required            // to obtain current a[i]            v[a[i]].push_back(cnt);        }    }     int ans = INT_MAX;     // Traverse v[] to obtain    // minimum count of moves    for (int i = 0; i < MAX; i++) {         // Check if there are at least        // K equal elements for v[i]        if (v[i].size() >= k) {             int move = 0;             sort(v[i].begin(), v[i].end());             // Add the sum of minimum K moves            for (int j = 0; j < k; j++) {                 move += v[i][j];            }             // Update answer            ans = min(ans, move);        }    }     // Return the final answer    return ans;} // Driver Codeint main(){    int N = 5, K = 3, D = 2;    vector<int> A = { 1, 2, 3, 4, 5 };     cout << getMinimumMoves(N, K, D, A);     return 0;}
// Java program to implement// the above approachimport java.util.*; class GFG{ // Function to return minimum// number of moves required@SuppressWarnings("unchecked")static int getMinimumMoves(int n, int k,                           int d, int[] a){    int MAX = 100000;     // Stores the number of moves    // required to obtain respective    // values from the given array    Vector<Integer> []v = new Vector[MAX];    for(int i = 0; i < v.length; i++)        v[i] = new Vector<Integer>();             // Traverse the array    for(int i = 0; i < n; i++)    {        int cnt = 0;         // Insert 0 into V[a[i]] as        // it is the initial state        v[a[i]].add(0);         while (a[i] > 0)        {            a[i] /= d;            cnt++;             // Insert the moves required            // to obtain current a[i]            v[a[i]].add(cnt);        }    }     int ans = Integer.MAX_VALUE;     // Traverse v[] to obtain    // minimum count of moves    for(int i = 0; i < MAX; i++)    {                 // Check if there are at least        // K equal elements for v[i]        if (v[i].size() >= k)        {            int move = 0;             Collections.sort(v[i]);             // Add the sum of minimum K moves            for(int j = 0; j < k; j++)            {                move += v[i].get(j);            }             // Update answer            ans = Math.min(ans, move);        }    }     // Return the final answer    return ans;} // Driver Codepublic static void main(String[] args){    int N = 5, K = 3, D = 2;    int []A = { 1, 2, 3, 4, 5 };     System.out.print(getMinimumMoves(N, K, D, A));}} // This code is contributed by Amit Katiyar
# Python3 program to implement# the above approach # Function to return minimum# number of moves requireddef getMinimumMoves(n, k, d, a):     MAX = 100000     # Stores the number of moves    # required to obtain respective    # values from the given array    v = []    for i in range(MAX):        v.append([])     # Traverse the array    for i in range(n):        cnt = 0         # Insert 0 into V[a[i]] as        # it is the initial state        v[a[i]] += [0]         while(a[i] > 0):            a[i] //= d            cnt += 1             # Insert the moves required            # to obtain current a[i]            v[a[i]] += [cnt]     ans = float('inf')     # Traverse v[] to obtain    # minimum count of moves    for i in range(MAX):         # Check if there are at least        # K equal elements for v[i]        if(len(v[i]) >= k):            move = 0            v[i].sort()             # Add the sum of minimum K moves            for j in range(k):                move += v[i][j]             # Update answer            ans = min(ans, move)     # Return the final answer    return ans # Driver Codeif __name__ == '__main__':     N = 5    K = 3    D = 2    A = [ 1, 2, 3, 4, 5 ]     # Function call    print(getMinimumMoves(N, K, D, A)) # This code is contributed by Shivam Singh
// C# program to implement// the above approachusing System;using System.Collections.Generic; class GFG{ // Function to return minimum// number of moves required static int getMinimumMoves(int n, int k,                           int d, int[] a){    int MAX = 100000;     // Stores the number of moves    // required to obtain respective    // values from the given array    List<int> []v = new List<int>[MAX];    for(int i = 0; i < v.Length; i++)        v[i] = new List<int>();             // Traverse the array    for(int i = 0; i < n; i++)    {        int cnt = 0;         // Insert 0 into V[a[i]] as        // it is the initial state        v[a[i]].Add(0);         while (a[i] > 0)        {            a[i] /= d;            cnt++;             // Insert the moves required            // to obtain current a[i]            v[a[i]].Add(cnt);        }    }     int ans = int.MaxValue;     // Traverse v[] to obtain    // minimum count of moves    for(int i = 0; i < MAX; i++)    {                 // Check if there are at least        // K equal elements for v[i]        if (v[i].Count >= k)        {            int move = 0;             v[i].Sort();             // Add the sum of minimum K moves            for(int j = 0; j < k; j++)            {                move += v[i][j];            }             // Update answer            ans = Math.Min(ans, move);        }    }     // Return the final answer    return ans;} // Driver Codepublic static void Main(String[] args){    int N = 5, K = 3, D = 2;    int []A = { 1, 2, 3, 4, 5 };     Console.Write(getMinimumMoves(N, K, D, A));}} // This code is contributed by 29AjayKumar
2
Time Complexity: O(MlogM), where M is the maximum number taken Auxiliary Space: O(M) 
SHIVAMSINGH67
amit143katiyar
29AjayKumar
the_raw_coder
saurabh1990aror
cpp-vector
frequency-counting
subset
Arrays
Mathematical
Matrix
Searching
Sorting
Arrays
Searching
Mathematical
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Matrix
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