Minimum number of squares whose sum equals to given number n

A number can always be represented as a sum of squares of other numbers. Note that 1 is a square and we can always break a number as (1*1 + 1*1 + 1*1 + …). Given a number n, find the minimum number of squares that sum to X.

Examples :

Input:  n = 100
Output: 1
100 can be written as 10². Note that 100 can also be 
written as 5² + 5² + 5² + 5², but this
representation requires 4 squares.

Input:  n = 6
Output: 3

Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

The idea is simple, we start from 1 and go till a number whose square is smaller than or equals to n. For every number x, we recur for n-x. Below is the recursive formula.

If n = 1 and x*x <= n

Below is a simple recursive solution based on above recursive formula.

C++

// A naive recursive C++ program to find minimum
// number of squares whose sum is equal to a given number
#include<bits/stdc++.h>
using namespace std;

// Returns count of minimum squares that sum to n
int getMinSquares(unsigned int n)
{
    // base cases
    if (n <= 3)
        return n;

    // getMinSquares rest of the table using recursive
    // formula
    int res = n; // Maximum squares required is n (1*1 + 1*1 + ..)

    // Go through all smaller numbers
    // to recursively find minimum
    for (int x = 1; x <= n; x++)
    {
        int temp = x*x;
        if (temp > n)
            break;
        else
            res =  min(res, 1+getMinSquares(n - temp));
    }
    return res;
}

// Driver program
int main()
{
    cout << getMinSquares(6);
    return 0;
}

Java

// A naive recursive JAVA program to find minimum
// number of squares whose sum is equal to a given number
class squares
{
    // Returns count of minimum squares that sum to n
    static int getMinSquares(int n)
    {
        // base cases
        if (n <= 3)
            return n;

        // getMinSquares rest of the table using recursive
        // formula
        int res = n; // Maximum squares required is
                     // n (1*1 + 1*1 + ..)

        // Go through all smaller numbers
        // to recursively find minimum
        for (int x = 1; x <= n; x++)
        {
            int temp = x*x;
            if (temp > n)
                break;
            else
                res =  Math.min(res, 1+getMinSquares(n - temp));
        }
        return res;
    }
    public static void main(String args[])
    {
        System.out.println(getMinSquares(6));
    }
}
/* This code is contributed by Rajat Mishra */

Python

# A naive recursive Python program to
# find minimum number of squares whose
# sum is equal to a given number

# Returns count of minimum squares 
# that sum to n
def getMinSquares(n):

    # base cases
    if n <= 3:
        return n;

    # getMinSquares rest of the table 
    # using recursive formula
    res = n # Maximum squares required 
            # is n (1*1 + 1*1 + ..)

    # Go through all smaller numbers
    # to recursively find minimum
    for x in range(1, n+1):
        temp = x * x;
        if temp > n:
            break
        else:
            res = min(res, 1 + getMinSquares(n 
                                  - temp))
    
    return res;

# Driver program 
print(getMinSquares(6))

# This code is contributed by nuclode

C#

// A naive recursive C# program
// to find minimum number of 
// squares whose sum is equal 
// to a given number
using System;

class GFG {
    
    // Returns count of minimum
    // squares that sum to n
    static int getMinSquares(int n)
    {
        
        // base cases
        if (n <= 3)
            return n;

        // getMinSquares rest of the
        // table using recursive
        // formula
        
        // Maximum squares required is
        // n (1*1 + 1*1 + ..)
        int res = n; 
        
        // Go through all smaller numbers
        // to recursively find minimum
        for (int x = 1; x <= n; x++)
        {
            int temp = x * x;
            if (temp > n)
                break;
            else
                res = Math.Min(res, 1 + getMinSquares(n - temp));
        }
        return res;
    }
    
    // Driver Code
    public static void Main()
    {
        Console.Write(getMinSquares(6));
    }
}

// This code is contributed by nitin mittal

PHP

<?php
// A naive recursive PHP program
// to find minimum number of 
// squares whose sum is equal 
// to a given number

// Returns count of minimum 
// squares that sum to n
function getMinSquares($n)
{
    // base cases
    if ($n <= 3)
        return $n;

    // getMinSquares rest of the 
    // table using recursive formula
    
    // Maximum squares required
    // is n (1*1 + 1*1 + ..)
    $res = $n; 

    // Go through all smaller numbers
    // to recursively find minimum
    for ($x = 1; $x <= $n; $x++)
    {
        $temp = $x * $x;
        if ($temp > $n)
            break;
        else
            $res = min($res, 1 + 
                       getMinSquares($n - 
                                     $temp));
    }
    return $res;
}

// Driver Code
echo getMinSquares(6);

// This code is contributed
// by nitin mittal.
?>

Output :

The time complexity of above solution is exponential. If we draw the complete recursion tree, we can observer that many subproblems are solved again and again. For example, when we start from n = 6, we can reach 4 by subtracting one 2 times and by subtracting 2 one times. So the subproblem for 4 is called twice.
Since same suproblems are called again, this problem has Overlapping Subprolems property. So min square sum problem has both properties (see this and this) of a dynamic programming problem. Like other typical Dynamic Programming(DP) problems, recomputations of same subproblems can be avoided by constructing a temporary array table[][] in bottom up manner. Below is Dynamic Programming based solution

C++

// A dynamic programming based C++ program to find minimum
// number of squares whose sum is equal to a given number
#include<bits/stdc++.h>
using namespace std;

// Returns count of minimum squares that sum to n
int getMinSquares(int n)
{
    // Create a dynamic programming table
    // to store sq
    int *dp = new int[n+1];

    // getMinSquares table for base case entries
    dp[0] = 0;
    dp[1] = 1;
    dp[2] = 2;
    dp[3] = 3;

    // getMinSquares rest of the table using recursive
    // formula
    for (int i = 4; i <= n; i++)
    {
        // max value is i as i can always be represented
        // as 1*1 + 1*1 + ...
        dp[i] = i;

        // Go through all smaller numbers to
        // to recursively find minimum
        for (int x = 1; x <= i; x++) {
            int temp = x*x;
            if (temp > i)
                break;
            else dp[i] = min(dp[i], 1+dp[i-temp]);
        }
    }

    // Store result and free dp[]
    int res = dp[n];
    delete [] dp;

    return res;
}

// Driver program
int main()
{
    cout << getMinSquares(6);
    return 0;
}

Java



// A dynamic programming based JAVA program to find minimum
// number of squares whose sum is equal to a given number
class squares
{
    // Returns count of minimum squares that sum to n
    static int getMinSquares(int n)
    {
        // Create a dynamic programming table
        // to store sq
        int dp[] = new int[n+1];
     
        // getMinSquares table for base case entries
        dp[0] = 0;
        dp[1] = 1;
        dp[2] = 2;
        dp[3] = 3;
     
        // getMinSquares rest of the table using recursive
        // formula
        for (int i = 4; i <= n; i++)
        {
            // max value is i as i can always be represented
            // as 1*1 + 1*1 + ...
            dp[i] = i;
     
            // Go through all smaller numbers to
            // to recursively find minimum
            for (int x = 1; x <= i; x++) {
                int temp = x*x;
                if (temp > i)
                    break;
                else dp[i] = Math.min(dp[i], 1+dp[i-temp]);
            }
        }
     
        // Store result and free dp[]
        int res = dp[n];
     
        return res;
    }
    public static void main(String args[])
    {
       System.out.println(getMinSquares(6));
    }
}/* This code is contributed by Rajat Mishra */

Python

# A dynamic programming based Python
# program to find minimum number of
# squares whose sum is equal to a 
# given number

# Returns count of minimum squares 
# that sum to n
def getMinSquares(n):

    # Create a dynamic programming table
    # to store sq and getMinSquares table
    # for base case entries
    dp = [0, 1, 2, 3]

    # getMinSquares rest of the table 
    # using recursive formula
    for i in range(4, n+1):
        
        # max value is i as i can always 
        # be represented as 1*1 + 1*1 + ...
        dp.append(i)

        # Go through all smaller numbers 
        # to recursively find minimum
        for x in range(1, i + 1):
            temp = x * x;
            if temp > i:
                break
            else:
                dp[i] = min(dp[i], 1 + 
                            dp[i-temp])

    # Store result
    return dp[n]

# Driver program
print(getMinSquares(6))

# This code is contributed by nuclode

C#


// A dynamic programming based 
// C# program to find minimum
// number of squares whose sum
// is equal to a given number
using System;

class squares
{
    // Returns count of minimum
    // squares that sum to n
    static int getMinSquares(int n)
    {
        // Create a dynamic programming
        // table to store sq
        int []dp = new int[n + 1];
    
        // getMinSquares table for base
        // case entries
        dp[0] = 0;
        dp[1] = 1;
        dp[2] = 2;
        dp[3] = 3;
    
        // getMinSquares for rest of the  
        // table using recursive formula
        for (int i = 4; i <= n; i++)
        {
            // max value is i as i can 
            // always be represented 
            // as 1 * 1 + 1 * 1 + ...
            dp[i] = i;
    
            // Go through all smaller numbers to
            // to recursively find minimum
            for (int x = 1; x <= i; x++) {
                int temp = x * x;
                if (temp > i)
                    break;
                else dp[i] = Math.Min(dp[i], 1 + 
                                      dp[i - temp]);
            }
        }
    
        // Store result and free dp[]
        int res = dp[n];
    
        return res;
    }
    
    // Driver Code
    public static void Main(String []args)
    {
    Console.Write(getMinSquares(6));
    }
}

// This code is contributed by Nitin Mittal.

Output:

Thanks to Gaurav Ahirwar for suggesting this solution.

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Practice Tags :

Dynamic Programming

Mathematical