【leetcode】171. Excel Sheet Column Number

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

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思路：
很简单，直接看代码就好。

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代码实现：

class Solution {
public:
    int char2Int(char c){
        return c-'A'+1;
    }
    
    int titleToNumber(string s) {
        int sum = char2Int(s[0]);
        
        for (int i = 1; i < s.size(); ++i){
            sum = sum * 26 + char2Int(s[i]);
        }
        
        return sum;
    }
};