# Count numbers with unit digit k in given range

Here given a range from low to high and given a number k.You have to find out the number of count which a number has same digit as k

Examples:

```Input : low = 2, high = 35, k = 2
Output : 4
Numbers are 2, 12, 22, 32.

Input  : low = 3, high = 30, k = 3
Output : 3
Numbers are  3, 13, 23.
```

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

A naive approach is to traverse through all numbers in given range and check last digit of every number and increment result if last digit is equal to k.

## C++

 `// Simple CPP program to count numbers with  ` `// last digit as k in given range. ` `#include ` `using` `namespace` `std; ` ` `  `// Returns count of numbers with k as last ` `// digit. ` `int` `counLastDigitK(``int` `low, ``int` `high, ``int` `k) ` `{ ` `    ``int` `count = 0; ` `    ``for` `(``int` `i = low; i <= high; i++)  ` `        ``if` `(i % 10 == k) ` `            ``count++;    ` `    ``return` `count; ` `} ` ` `  `// Driver Program ` `int` `main() ` `{ ` `    ``int` `low = 3, high = 35, k = 3; ` `    ``cout << counLastDigitK(low, high, k); ` `    ``return` `0; ` `} `

## Java

 `// Simple Java program to count numbers with  ` `// last digit as k in given range. ` `import` `java.util.*; ` `import` `java.lang.*; ` ` `  `public` `class` `GfG ` `{ ` `    ``// Returns count of numbers with ` `    ``// k as last digit. ` `    ``public` `static` `int` `counLastDigitK(``int` `low,  ` `                                ``int` `high, ``int` `k) ` `    ``{ ` `        ``int` `count = ``0``; ` `        ``for` `(``int` `i = low; i <= high; i++)  ` `            ``if` `(i % ``10` `== k) ` `                ``count++;  ` `        ``return` `count; ` `    ``} ` `     `  `    ``// driver function ` `    ``public` `static` `void` `main(String args[]) ` `    ``{ ` `        ``int` `low = ``3``, high = ``35``, k = ``3``; ` `        ``System.out.println(counLastDigitK(low, high, k)); ` `    ``} ` `} ` ` `  `// This code is contributed by Sagar Shukla `

## Python3

 `# Simple python program to count numbers with  ` `# last digit as k in given range. ` ` `  `# Returns count of numbers with k as last ` `# digit. ` `def` `counLastDigitK(low, high, k): ` `    ``count ``=` `0` `    ``for` `i ``in` `range``(low, high``+``1``): ` `        ``if` `(i ``%` `10` `=``=` `k): ` `            ``count``+``=``1`  `    ``return` `count ` ` `  ` `  `# Driver Program ` `low ``=` `3` `high ``=` `35` `k ``=` `3` `print``(counLastDigitK(low, high, k)) ` ` `  `# This code is contributed by ` `# Smitha Dinesh Semwal `

## C#

 `// Simple C# program to count numbers with  ` `// last digit as k in given range. ` `using` `System; ` ` `  `public` `class` `GfG ` `{ ` `    ``// Returns count of numbers with ` `    ``// k as last digit. ` `    ``public` `static` `int` `counLastDigitK(``int` `low,  ` `                                ``int` `high, ``int` `k) ` `    ``{ ` `        ``int` `count = 0; ` `        ``for` `(``int` `i = low; i <= high; i++)  ` `            ``if` `(i % 10 == k) ` `                ``count++;  ` `        ``return` `count; ` `    ``} ` `     `  `    ``// Driver function ` `    ``public` `static` `void` `Main() ` `    ``{ ` `        ``int` `low = 3, high = 35, k = 3; ` `        ``Console.WriteLine(counLastDigitK(low, high, k)); ` `    ``} ` `} ` ` `  `// This code is contributed by vt_m `

## PHP

 ` `

Output:

` 4`

Time Complexity : O(high – low)

An efficient solution is based on the fact that every digit appears once as last digit in every 10 consecutive numbers.

## C++

 `// Efficient CPP program to count numbers   ` `// with last digit as k in given range. ` `#include ` `using` `namespace` `std; ` ` `  `// Returns count of numbers with k as last ` `// digit. ` `int` `counLastDigitK(``int` `low, ``int` `high, ``int` `k) ` `{ ` `    ``int` `count = (high - low)/10; ` `    ``if` `(high % 10 >= k) ` `        ``count++; ` `    ``if` `(low % 10 > k) ` `        ``count--; ` `    ``return` `count; ` `} ` ` `  `// Driver Program ` `int` `main() ` `{ ` `    ``int` `low = 3, high = 35, k = 3; ` `    ``cout << counLastDigitK(low, high, k); ` `    ``return` `0; ` `} `

## Java

 `// Efficient Java program to count numbers  ` `// with last digit as k in given range. ` `import` `java.util.*; ` `import` `java.lang.*; ` ` `  `public` `class` `GfG ` `{ ` `    ``// Returns count of numbers with  ` `    ``// k as last digit. ` `    ``public` `static` `int` `counLastDigitK(``int` `low,  ` `                                 ``int` `high, ``int` `k) ` `    ``{ ` `        ``int` `count = (high - low)/``10``; ` `        ``if` `(high % ``10` `>= k) ` `            ``count++; ` `        ``if` `(low % ``10` `> k) ` `            ``count--; ` `        ``return` `count; ` `    ``} ` `     `  `    ``// driver function ` `    ``public` `static` `void` `main(String argc[]) ` `    ``{ ` `        ``int` `low = ``3``, high = ``35``, k = ``3``; ` `        ``System.out.println(counLastDigitK(low, high, k)); ` `    ``} ` `} ` ` `  `// This code is contributed by Sagar Shukla `

## Python3

 `# Efficient python program to count numbers  ` `# with last digit as k in given range. ` ` `  `# Returns count of numbers with k as last ` `# digit. ` `def` `counLastDigitK(low, high, k): ` `    ``count ``=` `(high ``-` `low)``/``10` `    ``if` `(high ``%` `10` `>``=` `k): ` `        ``count``+``=``1` `    ``if` `(low ``%` `10` `> k): ` `        ``count``-``=``1` `    ``return` `int``(count) ` ` `  ` `  `# Driver Program ` `low ``=` `3` `high ``=` `35` `k ``=` `3` `print``(counLastDigitK(low, high, k)) ` ` `  `# This code is contributed by ` `# Smitha Dinesh Semwal `

## C#

 `// Efficient Java program to count numbers  ` `// with last digit as k in given range. ` `using` `System; ` ` `  `public` `class` `GfG ` `{ ` `    ``// Returns count of numbers with  ` `    ``// k as last digit. ` `    ``public` `static` `int` `counLastDigitK(``int` `low,  ` `                                ``int` `high, ``int` `k) ` `    ``{ ` `        ``int` `count = (high - low) / 10; ` `        ``if` `(high % 10 >= k) ` `            ``count++; ` `        ``if` `(low % 10 > k) ` `            ``count--; ` `        ``return` `count; ` `    ``} ` `     `  `    ``// Driver function ` `    ``public` `static` `void` `Main() ` `    ``{ ` `        ``int` `low = 3, high = 35, k = 3; ` `        ``Console.WriteLine(counLastDigitK(low, high, k)); ` `    ``} ` `} ` ` `  `// This code is contributed by vt_m `

## PHP

 `= ``\$k``) ` `        ``\$count``++; ` `    ``if` `(``\$low` `% 10 > ``\$k``) ` `        ``\$count``--; ` `    ``return` `floor``(``\$count``); ` `} ` ` `  `// Driver Code ` `\$low` `= 3; ` `\$high` `= 35; ` `\$k` `= 3; ` `echo` `counLastDigitK(``\$low``,  ` `                    ``\$high``, ``\$k``); ` ` `  `// This code is contributed ` `// by ajit ` `?> `

Output:

` 4`

Time Complexity : O(1)

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Improved By : jit_t