Find total number of non-decreasing numbers with n digits in Python

In this tutorial, we’re going to learn how to find the total number of non-decreasing numbers with n digits in Python using the NumPy library. But first, we need to understand what a non-decreasing number is. A non-decreasing number is a number in which every digit (other than the first digit) is equal to or greater than its previous digit.

Also, we need to understand the utility of NumPy. NumPy is a special library in Python that can be implemented to use various mathematical functions, multi-dimensional arrays, etc. We need to explicitly import the NumPy library in Python using the ‘import’ command.

Let’s first check how to import NumPy library in Python:

import numpy as np;

 

Finding the total number of non-decreasing numbers in Python

import numpy as np;

def count(n) :  
  c=np.zeros((n+1,10));
  for i in range(10): 
    c[0][i] = 1;
  for i in range(1,n+1): 
    c[i][9]=1;
  for i in range(1,n+1): 
    for j in range(8,-1,-1): 
      c[i][j]=c[i-1][j]+c[i][j+1];
  result=int(c[n][0]);
  return result;


n=input("Enter number of digits:");
no=int(n);
print("Total no. of non-decreasing digits is ",count(no)) 

In this program, we are evaluating each of the numbers between a specified range and checking for the condition of the non-decreasing number. If the condition is satisfied, we’re counting the same. After executing the above code, we’ll find the total number of non-decreasing numbers with any number of digits.

Output generated will be:

Enter no. of digits: 3
Total no. of non-decreasing digits is 220