leetcode 168|171. Excel Sheet Column Title 171. Excel Sheet Column Number

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168. Excel Sheet Column Title

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

进制转换问题，给一个10进制，变为26进制，用A-Z表示
但是有点不一样， 26是Z。而不是进位。所以要分情况处理

先计算低位再计算高位。

class Solution {
public:
    string convertToTitle(int n) 
    {
        string ret = "";
        while (n != 0)
        {
            if(n % 26 != 0)
            {   
                ret = ret + char(n % 26 + 64); 
                n /= 26;
            }
            else
            {
                ret = ret + 'Z';
                n = n / 26 - 1;
            }
        }
        reverse(ret.begin(),ret.end());  
        return ret;     
    }
};

171. Excel Sheet Column Number

Related to question Excel Sheet Column Title

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) 
    {
        int ret = 0;
        int k = 1;
        while (s != "")
        {
            ret += k * (int(s[s.size()-1]) - 64);
            k *= 26;
            s = s.substr(0, s.size() - 1);       
        }
        return ret;  
    }
};