Leetcode 168: EXCEL sheet/ Leetcode 171: excel sheet II

Excel column转化的问题，其实excel上面计算column可以看做是 26 进制，这样26进制相互转化成10进制的问题就很好解决了。

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 

对于n 是26的整数倍的情况下，需要特殊处理，因为发现如果normal的10进制到26进制的转化是错误的。当n是26的整数倍的时候，n纪录的是还剩下多少个26在n中。

 class Solution {
public:
    string convertToTitle(int n) {
        string rst = "";
        while (n) {
            if (n % 26 == 0) {
                rst = 'Z' + rst;
                n = n/26-1;
            } else {
                char tmp = (n%26-1) + 'A';
                rst = tmp + rst;
                n = n/26;
            }
        }
        return rst;
    }
};

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

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