Given sum of digits 
and sum of square of digits 
. Find the smallest number with given sum of digits and sum of the square of digits. The number should not contain more than 100 digits. Print -1 if no such number exists or if the number of digits is more than 100.
Examples:
Input : a = 18, b = 162
Output : 99
Explanation : 99 is the smallest possible number whose sum of digits = 9 + 9 = 18 and sum of squares of digits is 92+92 = 162.Input : a = 12, b = 9
Output : -1
Approach:
Since the smallest number can be of 100 digits, it cannot be stored. Hence the first step to solve it will be to find the minimum number of digits which can give us the sum of digits as and sum of the square of digits as . To find the minimum number of digits, we can use Dynamic Programming. DP[a][b] signifies the minimum number of digits in a number whose sum of the digits will be and sum of the square of digits will be . If there does not exist any such number then DP[a][b] will be -1.
Since the number cannot exceed 100 digits, DP array will be of size 101*8101. Iterate for every digit, and try all possible combination of digits which gives us the sum of digits as and sum of the square of digits as . Store the minimum number of digits in DP[a][b] using the below recurrence relation:
DP[a][b] = min( minimumNumberOfDigits(a – i, b – (i * i)) + 1 )
where 1<=i<=9
After getting the minimum number of digits, find the digits. To find the digits, check for all combinations and print those digits which satisfies the condition below:
1 + dp[a – i][b – i * i] == dp[a][b]
where 1<=i<=9
If the condition above is met by any of i, reduce by i and by i*i and break. Keep on repeating the above process to find all the digits till is 0 and is 0.
Below is the implementation of above approach:
C++
// CPP program to find the Smallest number // with given sum of digits and // sum of square of digits #include <bits/stdc++.h> using namespace std; int dp[901][8101]; // Top down dp to find minimum number of digits with // given sum of dits a and sum of square of digits as b int minimumNumberOfDigits(int a, int b) { // Invalid condition if (a > b || a < 0 || b < 0 || a > 900 || b > 8100) return -1; // Number of digits satisfied if (a == 0 && b == 0) return 0; // Memoization if (dp[a][b] != -1) return dp[a][b]; // Initialize ans as maximum as we have to find the // minimum number of digits int ans = 101; // Check for all possible combinations of digits for (int i = 9; i >= 1; i--) { // recurrence call int k = minimumNumberOfDigits(a - i, b - (i * i)); // If the combination of digits cannot give sum as a // and sum of square of digits as b if (k != -1) ans = min(ans, k + 1); } // Returns the minimum number of digits return dp[a][b] = ans; } // Function to print the digits that gives // sum as a and sum of square of digits as b void printSmallestNumber(int a,int b) { // initialize the dp array as -1 memset(dp, -1, sizeof(dp)); // base condition dp[0][0] = 0; // function call to get the minimum number of digits int k = minimumNumberOfDigits(a, b); // When there does not exists any number if (k == -1 || k > 100) cout << "-1"; else { // Printing the digits from the most significant digit while (a > 0 && b > 0) { // Trying all combinations for (int i = 1; i <= 9; i++) { // checking conditions for minimum digits if (a >= i && b >= i * i && 1 + dp[a - i][b - i * i] == dp[a][b]) { cout << i; a -= i; b -= i * i; break; } } } } } // Driver Code int main() { int a = 18, b = 162; // Function call to print the smallest number printSmallestNumber(a,b); } |
Java
import java.util.Arrays; // Java program to find the Smallest number // with given sum of digits and // sum of square of digits class GFG { static int dp[][] = new int[901][8101]; // Top down dp to find minimum number of digits with // given sum of dits a and sum of square of digits as b static int minimumNumberOfDigits(int a, int b) { // Invalid condition if (a > b || a < 0 || b < 0 || a > 900 || b > 8100) { return -1; } // Number of digits satisfied if (a == 0 && b == 0) { return 0; } // Memoization if (dp[a][b] != -1) { return dp[a][b]; } // Initialize ans as maximum as we have to find the // minimum number of digits int ans = 101; // Check for all possible combinations of digits for (int i = 9; i >= 1; i--) { // recurrence call int k = minimumNumberOfDigits(a - i, b - (i * i)); // If the combination of digits cannot give sum as a // and sum of square of digits as b if (k != -1) { ans = Math.min(ans, k + 1); } } // Returns the minimum number of digits return dp[a][b] = ans; } // Function to print the digits that gives // sum as a and sum of square of digits as b static void printSmallestNumber(int a, int b) { // initialize the dp array as -1 for (int[] row : dp) { Arrays.fill(row, -1); } // base condition dp[0][0] = 0; // function call to get the minimum number of digits int k = minimumNumberOfDigits(a, b); // When there does not exists any number if (k == -1 || k > 100) { System.out.println("-1"); } else { // Printing the digits from the most significant digit while (a > 0 && b > 0) { // Trying all combinations for (int i = 1; i <= 9; i++) { // checking conditions for minimum digits if (a >= i && b >= i * i && 1 + dp[a - i][b - i * i] == dp[a][b]) { System.out.print(i); a -= i; b -= i * i; break; } } } } } // Driver Code public static void main(String args[]) { int a = 18, b = 162; // Function call to print the smallest number printSmallestNumber(a, b); } } // This code is contributed by PrinciRaj19992 |
Python3
# Python3 program to find the Smallest number # with given sum of digits and # sum of square of digits dp=[[-1 for i in range(8101)]for i in range(901)] # Top down dp to find minimum number of digits with # given sum of dits a and sum of square of digits as b def minimumNumberOfDigits(a,b): # Invalid condition if (a > b or a < 0 or b < 0 or a > 900 or b > 8100): return -1 # Number of digits satisfied if (a == 0 and b == 0): return 0 # Memoization if (dp[a][b] != -1): return dp[a][b] # Initialize ans as maximum as we have to find the # minimum number of digits ans = 101 #Check for all possible combinations of digits for i in range(9,0,-1): # recurrence call k = minimumNumberOfDigits(a - i, b - (i * i)) # If the combination of digits cannot give sum as a # and sum of square of digits as b if (k != -1): ans = min(ans, k + 1) # Returns the minimum number of digits dp[a][b] = ans return ans # Function to print the digits that gives # sum as a and sum of square of digits as b def printSmallestNumber(a,b): # initialize the dp array as for i in range(901): for j in range(8101): dp[i][j]=-1 # base condition dp[0][0] = 0 # function call to get the minimum number of digits k = minimumNumberOfDigits(a, b) # When there does not exists any number if (k == -1 or k > 100): print(-1,end='') else: # Printing the digits from the most significant digit while (a > 0 and b > 0): # Trying all combinations for i in range(1,10): #checking conditions for minimum digits if (a >= i and b >= i * i and 1 + dp[a - i][b - i * i] == dp[a][b]): print(i,end='') a -= i b -= i * i break# Driver Code if __name__=='__main__': a = 18 b = 162# Function call to print the smallest number printSmallestNumber(a,b) # This code is contributed by sahilshelangia |
C#
// C# program to find the Smallest number // with given sum of digits and // sum of square of digits using System; public class GFG { static int [,]dp = new int[901,8101]; // Top down dp to find minimum number of digits with // given sum of dits a and sum of square of digits as b static int minimumNumberOfDigits(int a, int b) { // Invalid condition if (a > b || a < 0 || b < 0 || a > 900 || b > 8100) { return -1; } // Number of digits satisfied if (a == 0 && b == 0) { return 0; } // Memoization if (dp[a,b] != -1) { return dp[a,b]; } // Initialize ans as maximum as we have to find the // minimum number of digits int ans = 101; // Check for all possible combinations of digits for (int i = 9; i >= 1; i--) { // recurrence call int k = minimumNumberOfDigits(a - i, b - (i * i)); // If the combination of digits cannot give sum as a // and sum of square of digits as b if (k != -1) { ans = Math.Min(ans, k + 1); } } // Returns the minimum number of digits return dp[a,b] = ans; } // Function to print the digits that gives // sum as a and sum of square of digits as b static void printSmallestNumber(int a, int b) { // initialize the dp array as -1 for (int i = 0; i < dp.GetLength(0); i++) for (int j = 0; j < dp.GetLength(1); j++) dp[i, j] = -1; // base condition dp[0,0] = 0; // function call to get the minimum number of digits int k = minimumNumberOfDigits(a, b); // When there does not exists any number if (k == -1 || k > 100) { Console.WriteLine("-1"); } else { // Printing the digits from the most significant digit while (a > 0 && b > 0) { // Trying all combinations for (int i = 1; i <= 9; i++) { // checking conditions for minimum digits if (a >= i && b >= i * i && 1 + dp[a - i,b - i * i] == dp[a,b]) { Console.Write(i); a -= i; b -= i * i; break; } } } } } // Driver Code public static void Main() { int a = 18, b = 162; // Function call to print the smallest number printSmallestNumber(a, b); } } // This code is contributed by PrinciRaj19992 |
99
Time Complexity : O(900*8100*9)
Auxiliary Space : O(900*8100)
Note: Time complexity is in terms of numbers as we are trying all possible combinations of digits.
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