# Reduce a given number to form a key by the given operations

Given an integer N, the task is to reduce the number and form a key by following the operations given below:

• Extract the Most Significant Digit of the number:
• If the digit is even: Add the consecutive digits until the sum of digits is odd.
• If the digit is odd: Add the consecutive digits until the sum of digits is even.
• Repeat the process for all the remaining digits.
• Finally, concatenate the sum computed together to get the key.

Examples:

Input: N = 1667848270
Output: 20290
Explanation:
Step 1: First Digit(= 1) is odd. So, add up the next digits until the sum is even.
Therefore, digits 1, 6, 6, and 7 are added up to form 20.
Step 2: Next digit(= 8) is even. So, add up the next digits until the sum is odd.
Therefore, digits 8, 4, 8, 2, and 7 are added up to form 29.
Step 3: Last digit(= 0) is even.
Therefore, the final answer after concatenating the results will be: 20290

Input: N = 7246262412
Output: 342
Explanation:
Step 1: First Digit(= 7) is odd. So, add up the next digits until the sum is even.
Therefore, digits 7, 2, 4, 6, 2, 6, 2, 4, and 1 are added up to form 34.
Step 2: Last digit(= 2) is even.
Therefore, the final answer after concatenating the results will be: 342.

Approach: The idea is to iterate the digits of the number and check the parity of the digit. If it is even, then proceed to the next digits until an odd digit is encountered. For odd digit, add consecutive digits until the sum of digits is even. Finally, concatenate the sum computed to get the desired key.

Below is the implementation of the above approach:

## C++

 `// C++ program of the` `// above approach` `#include ` `using` `namespace` `std;`   ` ``// Function to find the key` `// of the given number` `int` `key(``int` `N)` `{` `    `  `    ``// Convert the integer` `    ``// to String` `    ``string num = ``""` `+ to_string(N);` `    ``int` `ans = 0;` `    ``int` `j = 0;`   `    ``// Iterate the num-string` `    ``// to get the result` `    ``for``(j = 0; j < num.length(); j++)` `    ``{` `        `  `        ``// Check if digit is even or odd` `        ``if` `((num[j] - 48) % 2 == 0)` `        ``{` `            ``int` `add = 0;` `            ``int` `i;`   `            ``// Iterate until odd sum` `            ``// is obtained by adding` `            ``// consecutive digits` `            ``for``(i = j; j < num.length(); j++) ` `            ``{` `                ``add += num[j] - 48;`   `                ``// Check if sum becomes odd` `                ``if` `(add % 2 == 1)` `                    ``break``;` `            ``}`   `            ``if` `(add == 0)` `            ``{` `                ``ans *= 10;` `            ``}` `            ``else` `            ``{` `                ``int` `digit = (``int``)``floor``(``log10``(add) + 1);` `                ``ans *= (``pow``(10, digit));`   `                ``// Add the result in ans` `                ``ans += add;` `            ``}`   `            ``// Assign the digit index` `            ``// to num string` `            ``i = j;` `        ``}` `        ``else` `        ``{` `            `  `            ``// If the number is odd` `            ``int` `add = 0;` `            ``int` `i;`   `            ``// Iterate until odd sum` `            ``// is obtained by adding` `            ``// consecutive digits` `            ``for``(i = j; j < num.length(); j++)` `            ``{` `                ``add += num[j] - 48;`   `                ``// Check if sum becomes even` `                ``if` `(add % 2 == 0) ` `                ``{` `                    ``break``;` `                ``}` `            ``}`   `            ``if` `(add == 0) ` `            ``{` `                ``ans *= 10;` `            ``}` `            ``else` `            ``{` `                ``int` `digit = (``int``)``floor``(` `                       ``log10``(add) + 1);` `                ``ans *= (``pow``(10, digit));`   `                ``// Add the result in ans` `                ``ans += add;` `            ``}`   `            ``// assign the digit index` `            ``// to main numstring` `            ``i = j;` `        ``}` `    ``}`   `    ``// Check if all digits` `    ``// are visited or not` `    ``if` `(j + 1 >= num.length())` `    ``{` `        ``return` `ans;` `    ``}` `    ``else` `    ``{` `        ``return` `ans += num[num.length() - 1] - 48;` `    ``}` `}`   `// Driver code   ` `int` `main()` `{` `    ``int` `N = 1667848271;` `    `  `    ``cout << key(N);`   `    ``return` `0;` `}`   `// This code is contributed by divyeshrabadiya07`

## Java

 `// Java program of the` `// above approach`   `import` `java.io.*;` `import` `java.util.*;` `import` `java.lang.*;`   `public` `class` `Main {` `    ``// Function to find the key` `    ``// of the given number` `    ``static` `int` `key(``int` `N)` `    ``{`   `        ``// Convert the integer` `        ``// to String` `        ``String num = ``""` `+ N;` `        ``int` `ans = ``0``;` `        ``int` `j = ``0``;`   `        ``// Iterate the num-string` `        ``// to get the result` `        ``for` `(j = ``0``; j < num.length(); j++) {`   `            ``// Check if digit is even or odd` `            ``if` `((num.charAt(j) - ``48``) % ``2` `== ``0``) {` `                ``int` `add = ``0``;` `                ``int` `i;`   `                ``// Iterate until odd sum` `                ``// is obtained by adding` `                ``// consecutive digits` `                ``for` `(i = j; j < num.length(); j++) {` `                    ``add += num.charAt(j) - ``48``;`   `                    ``// Check if sum becomes odd` `                    ``if` `(add % ``2` `== ``1``)` `                        ``break``;` `                ``}`   `                ``if` `(add == ``0``) {` `                    ``ans *= ``10``;` `                ``}` `                ``else` `{` `                    ``int` `digit = (``int``)Math.floor(` `                        ``Math.log10(add) + ``1``);` `                    ``ans *= (Math.pow(``10``, digit));`   `                    ``// Add the result in ans` `                    ``ans += add;` `                ``}`   `                ``// Assign the digit index` `                ``// to num string` `                ``i = j;` `            ``}` `            ``else` `{` `                ``// If the number is odd` `                ``int` `add = ``0``;` `                ``int` `i;`   `                ``// Iterate until odd sum` `                ``// is obtained by adding` `                ``// consecutive digits` `                ``for` `(i = j; j < num.length(); j++) {` `                    ``add += num.charAt(j) - ``48``;`   `                    ``// Check if sum becomes even` `                    ``if` `(add % ``2` `== ``0``) {` `                        ``break``;` `                    ``}` `                ``}`   `                ``if` `(add == ``0``) {` `                    ``ans *= ``10``;` `                ``}` `                ``else` `{` `                    ``int` `digit = (``int``)Math.floor(` `                        ``Math.log10(add) + ``1``);` `                    ``ans *= (Math.pow(``10``, digit));`   `                    ``// Add the result in ans` `                    ``ans += add;` `                ``}`   `                ``// assign the digit index` `                ``// to main numstring` `                ``i = j;` `            ``}` `        ``}`   `        ``// Check if all digits` `        ``// are visited or not` `        ``if` `(j + ``1` `>= num.length()) {` `            ``return` `ans;` `        ``}` `        ``else` `{` `            ``return` `ans += num.charAt(` `                              ``num.length() - ``1``)` `                          ``- ``48``;` `        ``}` `    ``}`   `    ``// Driver Code` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``int` `N = ``1667848271``;` `        ``System.out.print(key(N));` `    ``}` `}`

## C#

 `// C# program of the` `// above approach` `using` `System;` `class` `GFG{` `   `  `// Function to find the key` `// of the given number` `static` `int` `key(``int` `N)` `{` `  ``// Convert the integer` `  ``// to String` `  ``String num = ``""` `+ N;` `  ``int` `ans = 0;` `  ``int` `j = 0;`   `  ``// Iterate the num-string` `  ``// to get the result` `  ``for` `(j = 0; j < num.Length; j++) ` `  ``{` `    ``// Check if digit is even or odd` `    ``if` `((num[j] - 48) % 2 == 0) ` `    ``{` `      ``int` `add = 0;` `      ``int` `i;`   `      ``// Iterate until odd sum` `      ``// is obtained by adding` `      ``// consecutive digits` `      ``for` `(i = j; j < num.Length; j++) ` `      ``{` `        ``add += num[j] - 48;`   `        ``// Check if sum becomes odd` `        ``if` `(add % 2 == 1)` `          ``break``;` `      ``}`   `      ``if` `(add == 0) ` `      ``{` `        ``ans *= 10;` `      ``}` `      ``else` `      ``{` `        ``int` `digit = (``int``)Math.Floor(` `                         ``Math.Log10(add) + 1);` `        ``ans *= (``int``)(Math.Pow(10, digit));`   `        ``// Add the result in ans` `        ``ans += add;` `      ``}`   `      ``// Assign the digit index` `      ``// to num string` `      ``i = j;` `    ``}` `    ``else` `    ``{` `      ``// If the number is odd` `      ``int` `add = 0;` `      ``int` `i;`   `      ``// Iterate until odd sum` `      ``// is obtained by adding` `      ``// consecutive digits` `      ``for` `(i = j; j < num.Length; j++) ` `      ``{` `        ``add += num[j] - 48;`   `        ``// Check if sum becomes even` `        ``if` `(add % 2 == 0) ` `        ``{` `          ``break``;` `        ``}` `      ``}`   `      ``if` `(add == 0) ` `      ``{` `        ``ans *= 10;` `      ``}` `      ``else` `{` `        ``int` `digit = (``int``)Math.Floor(` `                         ``Math.Log10(add) + 1);` `        ``ans *= (``int``)(Math.Pow(10, digit));`   `        ``// Add the result in ans` `        ``ans += add;` `      ``}`   `      ``// assign the digit index` `      ``// to main numstring` `      ``i = j;` `    ``}` `  ``}`   `  ``// Check if all digits` `  ``// are visited or not` `  ``if` `(j + 1 >= num.Length) ` `  ``{` `    ``return` `ans;` `  ``}` `  ``else` `  ``{` `    ``return` `ans += num[num.Length - 1] - 48;` `  ``}` `}`   `// Driver Code` `public` `static` `void` `Main(String[] args)` `{` `  ``int` `N = 1667848271;` `  ``Console.Write(key(N));` `}` `}`   `// This code is contributed by Rajput-Ji`

Output:

```20291

```

Time Complexity: O(N)
Auxiliary Space: O(1)

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