# Largest even digit number not greater than N

Given a number N, we need to write a program to find the largest number not greater than N which has all digits even.

Examples:

```Input: N = 23
Output: 22
Explanation: 22 is the largest number not
greater then N which has all digits even.

Input: N = 236
Output: 228
Explanation: 228 is the largest number not
greater than N which has all digits even.
```

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

Naive Approach: A naive approach is to iterate from N to 0, and find the first number which has all of its digits even.

Below is the implementation of the above approach:

## C++

 `// CPP program to print the largest ` `// integer not greater than N with all even digits ` `#include ` `using` `namespace` `std; ` ` `  `// function to check if all digits ` `// are even of a given number ` `int` `checkDigits(``int` `n) ` `{ ` `    ``// iterate for all digits ` `    ``while` `(n) { ` `        ``if` `((n % 10) % 2) ``// if digit is odd ` `            ``return` `0; ` ` `  `        ``n /= 10; ` `    ``} ` ` `  `    ``// all digits are even ` `    ``return` `1; ` `} ` ` `  `// function to return the largest number ` `// with all digits even ` `int` `largestNumber(``int` `n) ` `{ ` `    ``// iterate till we find a ` `    ``// number with all digits even ` `    ``for` `(``int` `i = n;; i--) ` `        ``if` `(checkDigits(i)) ` `            ``return` `i; ` `} ` ` `  `// Driver Code ` `int` `main() ` `{ ` `    ``int` `N = 23;     ` `    ``cout << largestNumber(N); ` `    ``return` `0; ` `} `

## Java

 `// Java program to print the largest ` `// integer not greater than N with  ` `// all even digits ` `import` `java .io.*; ` ` `  `public` `class` `GFG { ` `     `  `// function to check if all digits ` `// are even of a given number ` `static` `int` `checkDigits(``int` `n) ` `{ ` `     `  `    ``// iterate for all digits ` `    ``while` `(n > ``0``) ` `    ``{ ` `         `  `        ``// if digit is odd ` `        ``if` `(((n % ``10``) % ``2``) > ``0``)  ` `            ``return` `0``; ` ` `  `        ``n /= ``10``; ` `    ``} ` ` `  `    ``// all digits are even ` `    ``return` `1``; ` `} ` ` `  `// function to return the largest  ` `// number with all digits even ` `static` `int` `largestNumber(``int` `n) ` `{ ` `     `  `    ``// iterate till we find a ` `    ``// number with all digits even ` `    ``for` `(``int` `i = n;; i--) ` `        ``if` `(checkDigits(i) > ``0``) ` `            ``return` `i; ` `} ` ` `  `    ``// Driver Code ` `    ``static` `public` `void` `main (String[] args) ` `    ``{ ` `        ``int` `N = ``23``;  ` `        ``System.out.println(largestNumber(N)); ` `    ``} ` `} ` ` `  `// This code is contributed by vt_m. `

## Python3

 `# Python3 program to print the largest ` `# integer not greater than N with  ` `# all even digits ` ` `  `# function to check if all digits ` `# are even of a given number ` `def` `checkDigits(n): ` ` `  `     `  `    ``# iterate for all digits ` `    ``while` `(n>``0``):  ` `        ``# if digit is odd ` `        ``if` `((n ``%` `10``) ``%` `2``):  ` `            ``return` `False``; ` ` `  `        ``n ``=``int``(n``/``10``); ` ` `  `    ``# all digits are even ` `    ``return` `True``; ` ` `  `# function to return the ` `# largest number with ` `# all digits even ` `def` `largestNumber(n): ` `     `  `    ``# Iterate till we find a ` `    ``# number with all digits even ` `    ``for` `i ``in` `range``(n,``-``1``,``-``1``): ` `        ``if` `(checkDigits(i)): ` `            ``return` `i; ` ` `  `# Driver Code ` `N ``=` `23``;  ` `print``(largestNumber(N)); ` ` `  `# This code is contributed by mits `

## C#

 `// C# program to print the largest ` `// integer not greater than N with  ` `// all even digits ` `using` `System; ` ` `  `public` `class` `GFG { ` `     `  `// function to check if all digits ` `// are even of a given number ` `static` `int` `checkDigits(``int` `n) ` `{ ` `     `  `    ``// iterate for all digits ` `    ``while` `(n > 0) ` `    ``{ ` `         `  `        ``// if digit is odd ` `        ``if` `(((n % 10) % 2) > 0)  ` `            ``return` `0; ` ` `  `        ``n /= 10; ` `    ``} ` ` `  `    ``// all digits are even ` `    ``return` `1; ` `} ` ` `  `// function to return the largest  ` `// number with all digits even ` `static` `int` `largestNumber(``int` `n) ` `{ ` `     `  `    ``// iterate till we find a ` `    ``// number with all digits even ` `    ``for` `(``int` `i = n;; i--) ` `        ``if` `(checkDigits(i) > 0) ` `            ``return` `i; ` `} ` ` `  `    ``// Driver Code ` `    ``static` `public` `void` `Main () ` `    ``{ ` `        ``int` `N = 23;  ` `        ``Console.WriteLine(largestNumber(N)); ` `    ``} ` `} ` ` `  `// This code is contributed by aunj_67. `

## PHP

 ` `

Output:

`22`

Time Complexity: O(N)

Efficient Approach: We can obtain the required number by decreasing the first odd digit in N by one and then replacing all digits to the right of that odd digit with the largest even digit (i.e. 8). For example, if N = 24578, then X = 24488. In some cases, this approach can create a leading 0, we can simply drop the leading 0 in that case. For example, if N = 1334 then X = 0888. So, our answer will be X = 888. If there are no odd digits in N, then N is the number itself.

Below is the implementation of the above approach:

## C++

 `// CPP program to print the largest ` `// integer not greater than N with all even digits ` `#include ` `using` `namespace` `std; ` ` `  `// function to return the largest number ` `// with all digits even ` `int` `largestNumber(``int` `n) ` `{ ` `    ``string s = ``""``; ` `    ``int` `duplicate = n; ` ` `  `    ``// convert the number to a string for  ` `    ``// easy operations ` `    ``while` `(n) { ` `        ``s = ``char``(n % 10 + 48) + s; ` `        ``n /= 10; ` `    ``} ` ` `  `    ``int` `index = -1; ` ` `  `    ``// find first odd digit ` `    ``for` `(``int` `i = 0; i < s.length(); i++) { ` `        ``if` `((s[i] - ``'0'``) % 2 & 1) { ` `            ``index = i; ` `            ``break``; ` `        ``} ` `    ``} ` ` `  `    ``// if no digit, then N is the answer ` `    ``if` `(index == -1) ` `        ``return` `duplicate; ` ` `  `    ``int` `num = 0; ` ` `  `    ``// till first odd digit, add all even numbers ` `    ``for` `(``int` `i = 0; i < index; i++) ` `        ``num = num * 10 + (s[i] - ``'0'``); ` ` `  `    ``// decrease 1 from the odd digit ` `    ``num = num * 10 + (s[index] - ``'0'` `- 1); ` ` `  `    ``// add 0 in the rest of the digits ` `    ``for` `(``int` `i = index + 1; i < s.length(); i++) ` `        ``num = num * 10 + 8; ` ` `  `    ``return` `num; ` `} ` ` `  `// Driver Code ` `int` `main() ` `{ ` `    ``int` `N = 24578; ` ` `  `    ``cout << largestNumber(N); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java program to print the largest ` `// integer not greater than N with all even digits ` `class` `GFG ` `{ ` `     `  `// function to return the largest number ` `// with all digits even ` `static` `int` `largestNumber(``int` `n) ` `{ ` `    ``String s = ``""``; ` `    ``int` `duplicate = n; ` ` `  `    ``// convert the number to a string for  ` `    ``// easy operations ` `    ``while` `(n > ``0``)  ` `    ``{ ` `        ``s = (``char``)(n % ``10` `+ ``48``) + s; ` `        ``n /= ``10``; ` `    ``} ` ` `  `    ``int` `index = -``1``; ` ` `  `    ``// find first odd digit ` `    ``for` `(``int` `i = ``0``; i < s.length(); i++) ` `    ``{ ` `        ``if` `((((``int``)(s.charAt(i) - ``'0'``) % ``2``) & ``1``) > ``0``) ` `        ``{ ` `            ``index = i; ` `            ``break``; ` `        ``} ` `    ``} ` ` `  `    ``// if no digit, then N is the answer ` `    ``if` `(index == -``1``) ` `        ``return` `duplicate; ` ` `  `    ``int` `num = ``0``; ` ` `  `    ``// till first odd digit, add all even numbers ` `    ``for` `(``int` `i = ``0``; i < index; i++) ` `        ``num = num * ``10` `+ (``int``)(s.charAt(i) - ``'0'``); ` ` `  `    ``// decrease 1 from the odd digit ` `    ``num = num * ``10` `+ ((``int``)s.charAt(index) - (``int``)(``'0'``) - ``1``); ` ` `  `    ``// add 0 in the rest of the digits ` `    ``for` `(``int` `i = index + ``1``; i < s.length(); i++) ` `        ``num = num * ``10` `+ ``8``; ` ` `  `    ``return` `num; ` `} ` ` `  `// Driver Code ` `public` `static` `void` `main (String[] args) ` `{ ` `    ``int` `N = ``24578``; ` ` `  `    ``System.out.println(largestNumber(N)); ` `} ` `} ` ` `  `// This code is contributed by mits `

## Python3

 `# Python3 program to print the largest ` `# integer not greater than N with  ` `# all even digits ` `import` `math as mt ` ` `  `# function to return the largest  ` `# number with all digits even ` `def` `largestNumber(n): ` ` `  `    ``s ``=` `"" ` `    ``duplicate ``=` `n ` ` `  `    ``# convert the number to a string  ` `    ``# for easy operations ` `    ``while` `(n > ``0``): ` `        ``s ``=` `chr``(n ``%` `10` `+` `48``) ``+` `s ` `        ``n ``=` `n ``/``/` `10` `     `  `    ``index ``=` `-``1` ` `  `    ``# find first odd digit ` `    ``for` `i ``in` `range``(``len``(s)):  ` `        ``if` `((``ord``(s[i]) ``-` `ord``(``'0'``)) ``%` `2` `& ``1``): ` `            ``index ``=` `i ` `            ``break` `         `  `    ``# if no digit, then N is the answer ` `    ``if` `(index ``=``=` `-``1``): ` `        ``return` `duplicate ` ` `  `    ``num ``=` `0` ` `  `    ``# till first odd digit, add all  ` `    ``# even numbers ` `    ``for` `i ``in` `range``(index): ` `        ``num ``=` `num ``*` `10` `+` `(``ord``(s[i]) ``-` `ord``(``'0'``)) ` ` `  `    ``# decrease 1 from the odd digit ` `    ``num ``=` `num ``*` `10` `+` `(``ord``(s[index]) ``-`    `                      ``ord``(``'0'``) ``-` `1``) ` ` `  `    ``# add 0 in the rest of the digits ` `    ``for` `i ``in` `range``(index``+``1``,``len``(s)): ` `        ``num ``=` `num ``*` `10` `+` `8` ` `  `    ``return` `num ` ` `  `# Driver Code ` `N ``=` `24578` ` `  `print``(largestNumber(N)) ` ` `  `# This code is contributed  ` `# by Mohit kumar 29 ` `    `

## C#

 `// C# program to print the largest ` `// integer not greater than N with all even digits ` `using` `System; ` ` `  `class` `GFG ` `{ ` `     `  `// function to return the largest number ` `// with all digits even ` `static` `int` `largestNumber(``int` `n) ` `{ ` `    ``string` `s = ``""``; ` `    ``int` `duplicate = n; ` ` `  `    ``// convert the number to a string for  ` `    ``// easy operations ` `    ``while` `(n > 0)  ` `    ``{ ` `        ``s = (``char``)(n % 10 + 48) + s; ` `        ``n /= 10; ` `    ``} ` ` `  `    ``int` `index = -1; ` ` `  `    ``// find first odd digit ` `    ``for` `(``int` `i = 0; i < s.Length; i++) ` `    ``{ ` `        ``if` `((((``int``)(s[i] - ``'0'``) % 2) & 1) > 0) ` `        ``{ ` `            ``index = i; ` `            ``break``; ` `        ``} ` `    ``} ` ` `  `    ``// if no digit, then N is the answer ` `    ``if` `(index == -1) ` `        ``return` `duplicate; ` ` `  `    ``int` `num = 0; ` ` `  `    ``// till first odd digit, add all even numbers ` `    ``for` `(``int` `i = 0; i < index; i++) ` `        ``num = num * 10 + (``int``)(s[i] - ``'0'``); ` ` `  `    ``// decrease 1 from the odd digit ` `    ``num = num * 10 + ((``int``)s[index] - (``int``)(``'0'``) - 1); ` ` `  `    ``// add 0 in the rest of the digits ` `    ``for` `(``int` `i = index + 1; i < s.Length; i++) ` `        ``num = num * 10 + 8; ` ` `  `    ``return` `num; ` `} ` ` `  `// Driver Code ` `static` `void` `Main() ` `{ ` `    ``int` `N = 24578; ` ` `  `    ``Console.WriteLine(largestNumber(N)); ` `} ` `} ` ` `  `// This code is contributed by mits `

## PHP

 ` `

Output:

`24488`

Time Complexity: O(M), where M is the number of digits

My Personal Notes arrow_drop_up

Striver(underscore)79 at Codechef and codeforces D

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