[LeetCode] 171. Excel Sheet Column Number

[frdmu]

Given a string columnTitle that represents the 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
...
 

Example 1:

Input: columnTitle = "A"
Output: 1

Example 2:

Input: columnTitle = "AB"
Output: 28

Example 3:

Input: columnTitle = "ZY"
Output: 701

Example 4:

Input: columnTitle = "FXSHRXW"
Output: 2147483647

 

Constraints:

• 1 <= columnTitle.length <= 7
• columnTitle consists only of uppercase English letters.
• columnTitle is in the range ["A", "FXSHRXW"].

 
解法：
进制装换。代码如下：

class Solution {
public:
    int titleToNumber(string columnTitle) {
        int n = columnTitle.size();
        int res = 0; 
        long long mul = 1; 
        
        for (int i = n-1; i >= 0; i--) {
            res += (columnTitle[i]-'A'+1) * mul;
            mul *= 26;       
        }
        
        return res;
        
    }
};