# [171. Excel Sheet Column Number](https://leetcode.com/problems/excel-sheet-column-number/description/)
# 思路
第[168题](https://leetcode.com/problems/excel-sheet-column-title/description/)是将10进制转换为26进制，这题是将26进制转换为10进制.    
例：将k进制数"abcd"转换为10进制数：`res = d * k^0 + c * k^1 + b * k^2 + a * k^3`.
# C++
```
class Solution {
public:
    int titleToNumber(string s) {
        int res = 0, multiplier = 1;
        for(int i = s.size() - 1; i >= 0; i--){
            res += (int)(s[i] - 'A' + 1) * multiplier;
            multiplier *= 26;
        }
        return res;
    }
};
```