[leetcode] Excel Sheet Column Title & Excel Sheet Column Number

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 

思路：

10进制转26进制 。先求低位再求高位，与10进制转2进制一样。

题解：

class Solution {
public:
    string convertToTitle(int n) {
        string res;
        while(n) {
            n -= 1;
            char c = n%26+'A';
            res = c+res;
            n /= 26;
        }
        return res;
    }
};

Excel Sheet Column Number

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 

思路：

26进制转10进制，与2进制转10进制一样。

题解：

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