Remove minimum elements from either side such that 2*min becomes more than max (original) (raw)
Last Updated : 23 Jul, 2025
Given an unsorted array, trim the array such that twice of minimum is greater than maximum in the trimmed array. Elements should be removed either end of the array.
Number of removals should be minimum.
Examples:
arr[] = {4, 5, 100, 9, 10, 11, 12, 15, 200} Output: 4 We need to remove 4 elements (4, 5, 100, 200) so that 2*min becomes more than max.
arr[] = {4, 7, 5, 6} Output: 0 We don't need to remove any element as 4*2 > 7 (Note that min = 4, max = 8)
arr[] = {20, 7, 5, 6} Output: 1 We need to remove 20 so that 2*min becomes more than max
arr[] = {20, 4, 1, 3} Output: 3 We need to remove any three elements from ends like 20, 4, 1 or 4, 1, 3 or 20, 3, 1 or 20, 4, 1
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Naive Solution:
A naive solution is to try every possible case using recurrence. Following is the naive recursive algorithm. Note that the algorithm only returns minimum numbers of removals to be made, it doesn't print the trimmed array. It can be easily modified to print the trimmed array as well.
// Returns minimum number of removals to be made in // arr[l..h] minRemovals(int arr[], int l, int h)
- Find min and max in arr[l..h]
- If 2*min > max, then return 0.
- Else return minimum of "minRemovals(arr, l+1, h) + 1" and "minRemovals(arr, l, h-1) + 1"
Following is the implementation of above algorithm.
C++ `
// C++ implementation of above approach #include using namespace std;
// A utility function to find minimum of two numbers int min(int a, int b) {return (a < b)? a : b;}
// A utility function to find minimum in arr[l..h] int min(int arr[], int l, int h) { int mn = arr[l]; for (int i=l+1; i<=h; i++) if (mn > arr[i]) mn = arr[i]; return mn; }
// A utility function to find maximum in arr[l..h] int max(int arr[], int l, int h) { int mx = arr[l]; for (int i=l+1; i<=h; i++) if (mx < arr[i]) mx = arr[i]; return mx; }
// Returns the minimum number of removals from either end // in arr[l..h] so that 2min becomes greater than max. int minRemovals(int arr[], int l, int h) { // If there is 1 or less elements, return 0 // For a single element, 2min > max // (Assumption: All elements are positive in arr[]) if (l >= h) return 0;
// 1) Find minimum and maximum in arr[l..h]
int mn = min(arr, l, h);
int mx = max(arr, l, h);
//If the property is followed, no removals needed
if (2*mn > mx)
return 0;
// Otherwise remove a character from left end and recur,
// then remove a character from right end and recur, take
// the minimum of two is returned
return min(minRemovals(arr, l+1, h),
minRemovals(arr, l, h-1)) + 1;}
// Driver program to test above functions int main() { int arr[] = {4, 5, 100, 9, 10, 11, 12, 15, 200}; int n = sizeof(arr)/sizeof(arr[0]); cout << minRemovals(arr, 0, n-1); return 0; }
Java
// Java implementation of above approach import java.io.; import java.util.;
class GFG { // A utility function to find minimum of two numbers static int min(int a, int b) { return (a < b) ? a : b; }
// A utility function to find minimum in arr[l..h]
static int min(int arr[], int l, int h)
{
int mn = arr[l];
for (int i = l + 1; i <= h; i++)
if (mn > arr[i])
mn = arr[i];
return mn;
}
// A utility function to find maximum in arr[l..h]
static int max(int arr[], int l, int h)
{
int mx = arr[l];
for (int i = l + 1; i <= h; i++)
if (mx < arr[i])
mx = arr[i];
return mx;
}
// Returns the minimum number of removals from either
// end in arr[l..h] so that 2*min becomes greater than
// max.
static int minRemovals(int arr[], int l, int h)
{
// If there is 1 or less elements, return 0
// For a single element, 2*min > max
// (Assumption: All elements are positive in arr[])
if (l >= h)
return 0;
// 1) Find minimum and maximum in arr[l..h]
int mn = min(arr, l, h);
int mx = max(arr, l, h);
// If the property is followed, no removals needed
if (2 * mn > mx)
return 0;
// Otherwise remove a character from left end and
// recur, then remove a character from right end and
// recur, take the minimum of two is returned
return min(minRemovals(arr, l + 1, h),
minRemovals(arr, l, h - 1))
+ 1;
}
// Driver Code
public static void main(String[] args)
{
int arr[] = { 4, 5, 100, 9, 10, 11, 12, 15, 200 };
int n = arr.length;
System.out.print(minRemovals(arr, 0, n - 1));
}}
// This code is contributed by Mukul Singh.
Python3
Python3 implementation of above approach
A utility function to find
minimum in arr[l..h]
def mini(arr, l, h): mn = arr[l] for i in range(l + 1, h + 1): if (mn > arr[i]): mn = arr[i] return mn
A utility function to find
maximum in arr[l..h]
def max(arr, l, h): mx = arr[l] for i in range(l + 1, h + 1): if (mx < arr[i]): mx = arr[i] return mx
Returns the minimum number of
removals from either end in
arr[l..h] so that 2*min becomes
greater than max.
def minRemovals(arr, l, h):
# If there is 1 or less elements, return 0
# For a single element, 2*min > max
# (Assumption: All elements are positive in arr[])
if (l >= h):
return 0
# 1) Find minimum and maximum
# in arr[l..h]
mn = mini(arr, l, h)
mx = max(arr, l, h)
# If the property is followed,
# no removals needed
if (2 * mn > mx):
return 0
# Otherwise remove a character from
# left end and recur, then remove a
# character from right end and recur,
# take the minimum of two is returned
return (min(minRemovals(arr, l + 1, h),
minRemovals(arr, l, h - 1)) + 1)Driver Code
arr = [4, 5, 100, 9, 10, 11, 12, 15, 200] n = len(arr) print(minRemovals(arr, 0, n - 1))
This code is contributed
by sahilshelangia
C#
// C# implementation of above approach using System;
class GFG { // A utility function to find minimum of two numbers static int min(int a, int b) {return (a < b)? a : b;}
// A utility function to find minimum in arr[l..h] static int min(int[] arr, int l, int h) { int mn = arr[l]; for (int i=l+1; i<=h; i++) if (mn > arr[i]) mn = arr[i]; return mn; }
// A utility function to find maximum in arr[l..h] static int max(int[] arr, int l, int h) { int mx = arr[l]; for (int i=l+1; i<=h; i++) if (mx < arr[i]) mx = arr[i]; return mx; }
// Returns the minimum number of removals from either end // in arr[l..h] so that 2min becomes greater than max. static int minRemovals(int[] arr, int l, int h) { // If there is 1 or less elements, return 0 // For a single element, 2min > max // (Assumption: All elements are positive in arr[]) if (l >= h) return 0;
// 1) Find minimum and maximum in arr[l..h]
int mn = min(arr, l, h);
int mx = max(arr, l, h);
//If the property is followed, no removals needed
if (2*mn > mx)
return 0;
// Otherwise remove a character from left end and recur,
// then remove a character from right end and recur, take
// the minimum of two is returned
return min(minRemovals(arr, l+1, h),
minRemovals(arr, l, h-1)) + 1;}
// Driver Code public static void Main() { int[] arr = {4, 5, 100, 9, 10, 11, 12, 15, 200}; int n = arr.Length; Console.Write(minRemovals(arr, 0, n-1)); } }
// This code is contributed by Akanksha Rai
PHP
JavaScript
`
Time complexity: Time complexity of the above function can be written as following
T(n) = 2T(n-1) + O(n)
An upper bound on solution of above recurrence would be O(n x 2n).
Auxiliary Space: O(1)
Dynamic Programming:
The above recursive code exhibits many overlapping subproblems. For example minRemovals(arr, l+1, h-1) is evaluated twice. So Dynamic Programming is the choice to optimize the solution. Following is Dynamic Programming based solution.
C++ `
// C++ program of above approach #include using namespace std;
// A utility function to find minimum of two numbers int min(int a, int b) {return (a < b)? a : b;}
// A utility function to find minimum in arr[l..h] int min(int arr[], int l, int h) { int mn = arr[l]; for (int i=l+1; i<=h; i++) if (mn > arr[i]) mn = arr[i]; return mn; }
// A utility function to find maximum in arr[l..h] int max(int arr[], int l, int h) { int mx = arr[l]; for (int i=l+1; i<=h; i++) if (mx < arr[i]) mx = arr[i]; return mx; }
// Returns the minimum number of removals from either end // in arr[l..h] so that 2*min becomes greater than max. int minRemovalsDP(int arr[], int n) { // Create a table to store solutions of subproblems int table[n][n], gap, i, j, mn, mx;
// Fill table using above recursive formula. Note that the table
// is filled in diagonal fashion ,
// from diagonal elements to table[0][n-1] which is the result.
for (gap = 0; gap < n; ++gap)
{
for (i = 0, j = gap; j < n; ++i, ++j)
{
mn = min(arr, i, j);
mx = max(arr, i, j);
table[i][j] = (2*mn > mx)? 0: min(table[i][j-1]+1,
table[i+1][j]+1);
}
}
return table[0][n-1];}
// Driver program to test above functions int main() { int arr[] = {20, 4, 1, 3}; int n = sizeof(arr)/sizeof(arr[0]); cout << minRemovalsDP(arr, n); return 0; }
Java
// Java program of above approach import java.util.; import java.io.;
class GFG {
// A utility function to find minimum of two numbers static int min(int a, int b) { return (a < b) ? a : b; }
// A utility function to find minimum in arr[l..h] static int min(int arr[], int l, int h) { int mn = arr[l]; for (int i = l + 1; i <= h; i++) { if (mn > arr[i]) { mn = arr[i]; } } return mn; }
// A utility function to find maximum in arr[l..h] static int max(int arr[], int l, int h) { int mx = arr[l]; for (int i = l + 1; i <= h; i++) { if (mx < arr[i]) { mx = arr[i]; } } return mx; }
// Returns the minimum number of removals from either end // in arr[l..h] so that 2*min becomes greater than max. static int minRemovalsDP(int arr[], int n) { // Create a table to store solutions of subproblems int table[][] = new int[n][n], gap, i, j, mn, mx;
// Fill table using above recursive formula. Note that the table
// is filled in diagonal fashion (similar to https://www.geeksforgeeks.org/dsa/minimum-insertions-to-form-a-palindrome-dp-28/),
// from diagonal elements to table[0][n-1] which is the result.
for (gap = 0; gap < n; ++gap) {
for (i = 0, j = gap; j < n; ++i, ++j) {
mn = min(arr, i, j);
mx = max(arr, i, j);
table[i][j] = (2 * mn > mx) ? 0 : min(table[i][j - 1] + 1,
table[i + 1][j] + 1);
}
}
return table[0][n - 1];
}// Driver program to test above functions public static void main(String[] args) { int arr[] = {20, 4, 1, 3}; int n = arr.length; System.out.println(minRemovalsDP(arr, n));
}} // This code contributed by 29AJayKumar
Python3
Python3 program of above approach
A utility function to find
minimum in arr[l..h]
def min1(arr, l, h): mn = arr[l]; for i in range(l + 1,h+1): if (mn > arr[i]): mn = arr[i]; return mn;
A utility function to find
maximum in arr[l..h]
def max1(arr, l, h): mx = arr[l]; for i in range(l + 1, h + 1): if (mx < arr[i]): mx = arr[i]; return mx;
Returns the minimum number of removals
from either end in arr[l..h] so that
2*min becomes greater than max.
def minRemovalsDP(arr, n):
# Create a table to store
# solutions of subproblems
table = [[0 for x in range(n)] for y in range(n)];
# Fill table using above recursive formula.
# Note that the table is filled in diagonal fashion
# (similar to http:#goo.gl/PQqoS), from diagonal elements
# to table[0][n-1] which is the result.
for gap in range(n):
i = 0;
for j in range(gap,n):
mn = min1(arr, i, j);
mx = max1(arr, i, j);
table[i][j] = 0 if (2 * mn > mx) else min(table[i][j - 1] + 1,table[i + 1][j] + 1);
i += 1;
return table[0][n - 1];Driver Code
arr = [20, 4, 1, 3]; n = len(arr); print(minRemovalsDP(arr, n));
This code is contributed by mits
C#
// C# program of above approach using System;
public class GFG {
// A utility function to find minimum of two numbers
static int min(int a, int b) {
return (a < b) ? a : b;
}
// A utility function to find minimum in arr[l..h]
static int min(int []arr, int l, int h) {
int mn = arr[l];
for (int i = l + 1; i <= h; i++) {
if (mn > arr[i]) {
mn = arr[i];
}
}
return mn;
}// A utility function to find maximum in arr[l..h] static int max(int []arr, int l, int h) { int mx = arr[l]; for (int i = l + 1; i <= h; i++) { if (mx < arr[i]) { mx = arr[i]; } } return mx; }
// Returns the minimum number of removals from either end
// in arr[l..h] so that 2*min becomes greater than max.
static int minRemovalsDP(int []arr, int n) {
// Create a table to store solutions of subproblems
int [,]table = new int[n,n];
int gap, i, j, mn, mx;
// Fill table using above recursive formula. Note that the table
// is filled in diagonal fashion (similar to https://www.geeksforgeeks.org/dsa/minimum-insertions-to-form-a-palindrome-dp-28/),
// from diagonal elements to table[0][n-1] which is the result.
for (gap = 0; gap < n; ++gap) {
for (i = 0, j = gap; j < n; ++i, ++j) {
mn = min(arr, i, j);
mx = max(arr, i, j);
table[i,j] = (2 * mn > mx) ? 0 : min(table[i,j - 1] + 1,
table[i + 1,j] + 1);
}
}
return table[0,n - 1];
}
// Driver program to test above functions
public static void Main() {
int []arr = {20, 4, 1, 3};
int n = arr.Length;
Console.WriteLine(minRemovalsDP(arr, n));
}} // This code contributed by 29AJayKumar
PHP
JavaScript
`
Time Complexity: O(n3) where n is the number of elements in arr[].
Auxiliary Space: O(n^2)
Further Optimizations:
The above code can be optimized in many ways.
- We can avoid calculation of min() and/or max() when min and/or max is/are not changed by removing corner elements.
- We can pre-process the array and build segment tree in O(n) time. After the segment tree is built, we can query range minimum and maximum in O(Logn) time. The overall time complexity is reduced to O(n2Logn) time.
A O(n^2) Solution:
The idea is to find the maximum sized subarray such that 2*min > max. We run two nested loops, the outer loop chooses a starting point and the inner loop chooses ending point for the current starting point. We keep track of longest subarray with the given property.
Following is the implementation of the above approach. Thanks to Richard Zhang for suggesting this solution.
C++ `
// A O(n*n) solution to find the minimum of elements to // be removed #include #include using namespace std;
// Returns the minimum number of removals from either end // in arr[l..h] so that 2min becomes greater than max. int minRemovalsDP(int arr[], int n) { // Initialize starting and ending indexes of the maximum // sized subarray with property 2min > max int longest_start = -1, longest_end = 0;
// Choose different elements as starting point
for (int start=0; start<n; start++)
{
// Initialize min and max for the current start
int min = INT_MAX, max = INT_MIN;
// Choose different ending points for current start
for (int end = start; end < n; end ++)
{
// Update min and max if necessary
int val = arr[end];
if (val < min) min = val;
if (val > max) max = val;
// If the property is violated, then no
// point to continue for a bigger array
if (2 * min <= max) break;
// Update longest_start and longest_end if needed
if (end - start > longest_end - longest_start ||
longest_start == -1)
{
longest_start = start;
longest_end = end;
}
}
}
// If not even a single element follow the property,
// then return n
if (longest_start == -1) return n;
// Return the number of elements to be removed
return (n - (longest_end - longest_start + 1));}
// Driver program to test above functions int main() { int arr[] = {4, 5, 100, 9, 10, 11, 12, 15, 200}; int n = sizeof(arr)/sizeof(arr[0]); cout << minRemovalsDP(arr, n); return 0; }
Java
// A O(nn) solution to find the minimum of elements to // be removed import java.util.; import java.io.*;
class GFG {
// Returns the minimum number of removals from either end // in arr[l..h] so that 2min becomes greater than max. static int minRemovalsDP(int arr[], int n) { // Initialize starting and ending indexes of the maximum // sized subarray with property 2min > max int longest_start = -1, longest_end = 0;
// Choose different elements as starting point
for (int start = 0; start < n; start++) {
// Initialize min and max for the current start
int min = Integer.MAX_VALUE, max = Integer.MIN_VALUE;
// Choose different ending points for current start
for (int end = start; end < n; end++) {
// Update min and max if necessary
int val = arr[end];
if (val < min) {
min = val;
}
if (val > max) {
max = val;
}
// If the property is violated, then no
// point to continue for a bigger array
if (2 * min <= max) {
break;
}
// Update longest_start and longest_end if needed
if (end - start > longest_end - longest_start
|| longest_start == -1) {
longest_start = start;
longest_end = end;
}
}
}
// If not even a single element follow the property,
// then return n
if (longest_start == -1) {
return n;
}
// Return the number of elements to be removed
return (n - (longest_end - longest_start + 1));
}// Driver program to test above functions public static void main(String[] args) { int arr[] = {4, 5, 100, 9, 10, 11, 12, 15, 200}; int n = arr.length; System.out.println(minRemovalsDP(arr, n)); } }
// This code is contributed by PrinciRaj1992
Python3
A O(n*n) solution to find the minimum of
elements to be removed
import sys;
Returns the minimum number of removals
from either end in arr[l..h] so that
2*min becomes greater than max.
def minRemovalsDP(arr, n):
# Initialize starting and ending indexes
# of the maximum sized subarray
# with property 2*min > max
longest_start = -1;
longest_end = 0;
# Choose different elements as starting point
for start in range(n):
# Initialize min and max
# for the current start
min = sys.maxsize;
max = -sys.maxsize;
# Choose different ending points for current start
for end in range(start,n):
# Update min and max if necessary
val = arr[end];
if (val < min):
min = val;
if (val > max):
max = val;
# If the property is violated, then no
# point to continue for a bigger array
if (2 * min <= max):
break;
# Update longest_start and longest_end if needed
if (end - start > longest_end - longest_start or longest_start == -1):
longest_start = start;
longest_end = end;
# If not even a single element follow the property,
# then return n
if (longest_start == -1):
return n;
# Return the number of elements to be removed
return (n - (longest_end - longest_start + 1));Driver Code
arr = [4, 5, 100, 9, 10, 11, 12, 15, 200]; n = len(arr); print(minRemovalsDP(arr, n));
This code is contributed by mits
C#
// A O(n*n) solution to find the minimum of elements to // be removed
using System; public class GFG {
// Returns the minimum number of removals from either end // in arr[l..h] so that 2min becomes greater than max. static int minRemovalsDP(int []arr, int n) { // Initialize starting and ending indexes of the maximum // sized subarray with property 2min > max int longest_start = -1, longest_end = 0;
// Choose different elements as starting point
for (int start = 0; start < n; start++) {
// Initialize min and max for the current start
int min = int.MaxValue, max = int.MinValue;
// Choose different ending points for current start
for (int end = start; end < n; end++) {
// Update min and max if necessary
int val = arr[end];
if (val < min) {
min = val;
}
if (val > max) {
max = val;
}
// If the property is violated, then no
// point to continue for a bigger array
if (2 * min <= max) {
break;
}
// Update longest_start and longest_end if needed
if (end - start > longest_end - longest_start
|| longest_start == -1) {
longest_start = start;
longest_end = end;
}
}
}
// If not even a single element follow the property,
// then return n
if (longest_start == -1) {
return n;
}
// Return the number of elements to be removed
return (n - (longest_end - longest_start + 1));
}// Driver program to test above functions public static void Main() { int []arr = {4, 5, 100, 9, 10, 11, 12, 15, 200}; int n = arr.Length; Console.WriteLine(minRemovalsDP(arr, n)); } }
// This code is contributed by Rajput-Ji
PHP
JavaScript
`
Time Complexity: O(N2)
Auxiliary Space: O(1)