【LeetCode】171. Excel Sheet Column Number && 168. Excel Sheet Column Title

171.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) {
if(s.size()==0) return 0;
int result = 0;
for(int i =0; i < s.length(); i++)
{
int tmp = s[i] - 64;
result += pow(26,s.length()-i-1)*tmp;
}
return result;

}
};

168.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

class Solution {
public:
//本质是从一个10进制数转换成26进制,由于下标从1开始而不是从0开始，因此要减一操作
string convertToTitle(int n) {
string s="";
if(n <=0) return 0;
while(n>0)
{
int tmp = (n-1)%26;
s += tmp + 65;
n = (n-1) / 26;
}
reverse(s.begin(),s.end());
return s;

}
};