Excel Sheet Column Title Leetcode Solution

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Excel Sheet Column Title Leetcode Solution
Excel Sheet Column Title Leetcode Solution

Problem Statement
In this problem a positive integer is given which represents a column number of an Excel sheet, we have to return its corresponding column title as appear in an Excel sheet.

Example
#1
28
"AB"
#2
701
"ZY"
Approach
This problem is the reverse of the problem in which we have to find out the column number from a column title.
So in that problem we converted a base-26 number into base-10 number which is a decimal number. In this problem we have to find out column title from column number. So here we just have to do opposite, i.e. we have to convert a base-10 (decimal) number into a number of base-26 system.

We know in general number system of suppose base-26 should have 26 characters which represents values 0 to 25. But in Excel sheet column title this is little different. It represents values from 1 to 26. So if we use characters A-Z as 0-25, then it will look like below equation:

Let string be ABZ, this is corresponding to number n:
n = (A+1) * 26^2 + (B+1) * 26^1 + (Z+1) * 26^0

Why (A+1)? Because in char system 'A' is 0, but in excel system 'A' is one. Every char get an extra one.

So in order to get last char i.e. Z we would first minus 1 i.e. n-- and then get n%26
(n-1)%26 = Z
Now divide with 26 and repeat same process for next character.
(n-1)/26 = (A+1) * 26^1 + (B+1) * 26^0
Algorithm

- Create an empty string for storing the characters.
- Run a loop while n is positive.

- Subtract 1 from n.

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Taken on: January 27, 2021
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