https://leetcode.com/problems/excel-sheet-column-title/#/description
Given a positive integer, return its corresponding column title as appear in an Excel sheet.
For example:
1 -> A
2 -> B
3 -> C
...
26 -> Z
27 -> AA
28 -> AB
Sol:
For input number, we take the remainder of it divided by 26, then use the remainder from 0 to 25 to append a corresponding capital letter to an empty list. Then update the number to number// 26 to find the next capital letter.
Finally, we output the list in a reverse manner.
class Solution(object): def convertToTitle(self, num): """ :type n: int :rtype: str """ # return a string # ABCD＝A×26³＋B×26²＋C×26¹＋D＝1×26³＋2×26²＋3×26¹＋4. # But how to get the column title from the number? We can't simply use the n%26 method because: ZZZZ＝Z×26³＋Z×26²＋Z×26¹＋Z＝26×26³＋26×26²＋26×26¹＋26 # We can use (n-1)%26 instead, then we get a number range from 0 to 25. capitals = [chr(x) for x in range(ord('A'), ord('Z') + 1)] result = [] while num > 0: result.append(capitals[(num - 1)%26]) num = (num-1) // 26 result.reverse() return ''.join(result)
Note:
1 The reseason why we use (num - 1) % 26 rather than num % 26 to encode is that:
(num - 1) % 26
for i in range(1, 26+1):
print i % 26
==>
1
2
3
...
25
0
It is not convienent to use them as the indice as the array[ABCDEF...Z]
However,
num % 26
for j in range(0, 25+1):
print j %26
==>
0
1
2
...
25