C Programming: Count unique digits of integers

Last update on August 07 2025 12:49:38 (UTC/GMT +8 hours)

37. Count Unique Digit Numbers Variants

Write a C program that counts the number of integers whose digits are unique from 1 and a given integer value.

Example:
Input: n = 30
From 1 to 30 all the integers have unique digits, except 11 and 22
Output: 28

Test Data:
(30) -> 28
(135) -> 110

Sample Solution:

C Code:

#include <stdio.h>
#include <math.h>

// Function to count unique digits in an integer 'n'
int test(int n) {
  // Calculate the length of the integer 'n'
  int len = floor(log10(abs(n))) + 1;
  int temp, i;
  int count = 0;
  int data[10] = { 0 }; // Array to store occurrences of digits (0-9)

  // Extract digits from 'n' and count their occurrences
  while (n > 0) {
    temp = n % 10;
    n = n / 10;
    data[temp]++;
  }

  // Count unique digits (digits that occurred exactly once)
  for (i = 0; i < 10; ++i) {
    if (data[i] == 1)
      count++;
  }

  // Check if the count of unique digits equals the length of 'n'
  if (count == len)
    return len; // Return the length if all digits are unique
  else
    return 0; // Return 0 if not all digits are unique
}

// Main function
int main(void) {
  int n = 135, ctr = 0, result;

  // Loop through integers from 1 to 'n' to count unique digits using the 'test' function
  for (int i = 1; i <= n; i++) {
    result = test(i);
    if (result > 0) {
      ctr++; // Increment counter if unique digits are found
      result = 0;
    }
  }

  // Display the count of integers with unique digits in the specified range
  printf("Unique digits of integers from 1 and %d = %d", n, ctr);
}

Sample Output:

Unique digits of integers from 1 and 135 = 110

Flowchart:

$Flowchart: Count unique digits of integers$

For more Practice: Solve these Related Problems:

Write a C program to count numbers from 1 to n that have all unique digits using combinatorial methods.
Write a C program to generate and count numbers with unique digits without converting them to strings.
Write a C program to recursively determine if a number has unique digits and count how many do.
Write a C program to list all numbers with unique digits in a given range and return the total count.

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