[leetcode]Excel Sheet Column Number

本质是26进制，注意每次+1.

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