# Print all numbers less than N with at-most 2 unique digits

Given a number N(less than 10^9). The task is to print all the numbers less than N which are having a maximum of 2 unique digits.

Note: Number such as 100, 111, 101 are valid as the number of unique digits are at most 2 but 123 is invalid as it has 3 unique digits.

Examples:

Input: N = 12
Output: The numbers are: 1 2 3 4 5 6 7 8 9 10 11

Input: N = 154
Output: The numbers are: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 110 111 112 113 114 115 116 117 118 119 121 122 131 133 141 144 151

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:

• Since we are said a maximum of two unique digits, two loops will give us all combination of two digits.
• A recursive function is written in terms to generate all the numbers using two digits.
• Call the function with num initially as 0, and generate numbers using recurrence num*10+a and num*10+b, with the base case being num>=n.
• A set can be used to store all the numbers as there can be duplicate elements which the recursion function generates.

Below is the implementation of the above approach:

## C++

 `// C++ program to print all the numbers ` `// less than N which have at most 2 unique digits ` `#include ` `using` `namespace` `std; ` ` `  `set<``int``> st; ` ` `  `// Function to generate all possible numbers ` `void` `generateNumbers(``int` `n, ``int` `num, ``int` `a, ``int` `b) ` `{ ` `    ``// If the number is less than n ` `    ``if` `(num > 0 && num < n) ` `        ``st.insert(num); ` ` `  `    ``// If the number exceeds ` `    ``if` `(num >= n) ` `        ``return``; ` ` `  `    ``// Check if it is not the same number ` `    ``if` `(num * 10 + a > num) ` `        ``generateNumbers(n, num * 10 + a, a, b); ` ` `  `    ``generateNumbers(n, num * 10 + b, a, b); ` `} ` ` `  `// Function to print all numbers ` `void` `printNumbers(``int` `n) ` `{ ` `    ``// All combination of digits ` `    ``for` `(``int` `i = 0; i <= 9; i++) ` `        ``for` `(``int` `j = i + 1; j <= 9; j++) ` `            ``generateNumbers(n, 0, i, j); ` ` `  `    ``cout << ``"The numbers are: "``; ` ` `  `    ``// Print all numbers ` `    ``while` `(!st.empty()) { ` `        ``cout << *st.begin() << ``" "``; ` `        ``st.erase(st.begin()); ` `    ``} ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `n = 12; ` ` `  `    ``printNumbers(n); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java program to print all the numbers  ` `// less than N which have at most 2 unique digits  ` `import` `java.util.*; ` `class` `GFG{ ` `   `  `static` `Set st= ``new` `HashSet();  ` `   `  `// Function to generate all possible numbers  ` `static` `void` `generateNumbers(``int` `n, ``int` `num, ``int` `a, ``int` `b)  ` `{  ` `    ``// If the number is less than n  ` `    ``if` `(num > ``0` `&& num < n)  ` `        ``st.add(num);  ` `   `  `    ``// If the number exceeds  ` `    ``if` `(num >= n)  ` `        ``return``;  ` `   `  `    ``// Check if it is not the same number  ` `    ``if` `(num * ``10` `+ a > num)  ` `        ``generateNumbers(n, num * ``10` `+ a, a, b);  ` `   `  `    ``generateNumbers(n, num * ``10` `+ b, a, b);  ` `}  ` `   `  `// Function to print all numbers  ` `static` `void` `printNumbers(``int` `n)  ` `{  ` `    ``// All combination of digits  ` `    ``for` `(``int` `i = ``0``; i <= ``9``; i++)  ` `        ``for` `(``int` `j = i + ``1``; j <= ``9``; j++)  ` `            ``generateNumbers(n, ``0``, i, j);  ` `   `  `    ``System.out.print( ``"The numbers are: "``);  ` `   `  `    ``// Print all numbers  ` `    ``System.out.print(st); ` `     `  `    ``st.clear(); ` `}  ` `   `  `// Driver code  ` `public` `static` `void` `main(String args[])  ` `{  ` `    ``int` `n = ``12``;  ` `   `  `    ``printNumbers(n);  ` `   `  `}  ` `} ` `// This code is contributed by Arnab Kundu `

## Python3

 `# Python 3 program to print all the  ` `# numbers less than N which have at  ` `# most 2 unique digits ` `st ``=` `set``() ` ` `  `# Function to generate all possible numbers ` `def` `generateNumbers(n, num, a, b): ` `     `  `    ``# If the number is less than n ` `    ``if` `(num > ``0` `and` `num < n): ` `        ``st.add(num) ` ` `  `    ``# If the number exceeds ` `    ``if` `(num >``=` `n): ` `        ``return` ` `  `    ``# Check if it is not the same number ` `    ``if` `(num ``*` `10` `+` `a > num): ` `        ``generateNumbers(n, num ``*` `10` `+` `a, a, b) ` ` `  `    ``generateNumbers(n, num ``*` `10` `+` `b, a, b) ` ` `  `# Function to print all numbers ` `def` `printNumbers(n): ` `     `  `    ``# All combination of digits ` `    ``for` `i ``in` `range``(``10``): ` `        ``for` `j ``in` `range``(i ``+` `1``, ``10``, ``1``): ` `            ``generateNumbers(n, ``0``, i, j) ` ` `  `    ``print``(``"The numbers are:"``, end ``=` `" "``) ` `     `  `    ``# Print all numbers ` `    ``l ``=` `list``(st) ` `    ``for` `i ``in` `l: ` `        ``print``(i, end ``=` `" "``) ` ` `  `# Driver code ` `if` `__name__ ``=``=` `'__main__'``: ` `    ``n ``=` `12` ` `  `    ``printNumbers(n) ` ` `  `# This code is contributed by ` `# Shashank_Sharma `

## C#

 `// C# program to print all the numbers  ` `// less than N which have at most 2 unique digits  ` `using` `System; ` `using` `System.Collections.Generic; ` ` `  `class` `GFG ` `{ ` `     `  `static` `SortedSet<``int``> st = ``new` `SortedSet<``int``>();  ` `     `  `// Function to generate all possible numbers  ` `static` `void` `generateNumbers(``int` `n, ``int` `num, ``int` `a, ``int` `b)  ` `{  ` `    ``// If the number is less than n  ` `    ``if` `(num > 0 && num < n)  ` `        ``st.Add(num);  ` `     `  `    ``// If the number exceeds  ` `    ``if` `(num >= n)  ` `        ``return``;  ` `     `  `    ``// Check if it is not the same number  ` `    ``if` `(num * 10 + a > num)  ` `        ``generateNumbers(n, num * 10 + a, a, b);  ` `     `  `    ``generateNumbers(n, num * 10 + b, a, b);  ` `}  ` `     `  `// Function to print all numbers  ` `static` `void` `printNumbers(``int` `n)  ` `{  ` `    ``// All combination of digits  ` `    ``for` `(``int` `i = 0; i <= 9; i++)  ` `        ``for` `(``int` `j = i + 1; j <= 9; j++)  ` `            ``generateNumbers(n, 0, i, j);  ` `     `  `    ``Console.Write( ``"The numbers are: "``);  ` `     `  `    ``// Print all numbers  ` `    ``foreach``(``int` `obj ``in` `st) ` `        ``Console.Write(obj+``" "``); ` `     `  `    ``st.Clear(); ` `}  ` `     `  `// Driver code  ` `public` `static` `void` `Main(String []args)  ` `{  ` `    ``int` `n = 12;  ` `     `  `    ``printNumbers(n);  ` `}  ` `} ` ` `  `// This code has been contributed by 29AjayKumar `

Output:

```The numbers are: 1 2 3 4 5 6 7 8 9 10 11
```

Time complexity: O(36* 230) My Personal Notes arrow_drop_up Check out this Author's contributed articles.

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