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

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;      }};