171. Excel Sheet Column Number

https://leetcode.com/problems/excel-sheet-column-number/

Problem

Given a column title as appear in an Excel sheet, return its corresponding column number.

For example:

    A -> 1
    B -> 2
    C -> 3
    ...
    Z -> 26
    AA -> 27
    AB -> 28 
    ...

Example 1:

Input: "A"
Output: 1

Example 2:

Input: "AB"
Output: 28

Example 3:

Input: "ZY"
Output: 701

Constraints:

• 1 <= s.length <= 7

• s consists only of uppercase English letters.

• s is between "A" and "FXSHRXW".

Solution

1. Normal

class Solution {
public:
    int titleToNumber(string &s) {
        int number = 0;
        int multiplier = 1;
        for (int i = s.size() - 1; i >= 0; --i) {
            number += (s[i] - 'A' + 1) * multiplier;
            if (i > 0) multiplier *= 26;
        }
        return number;
    }
};

2. Optimized

class Solution {
public:
    int titleToNumber(string &s) {
        int result = 0;
        for (const auto& c: s)
            result = result * 26 + (c - 'A' + 1);
        return result;
    }
};

• #math

• #important

• #encoding