171-Excel表列序号

LeetCode 171. Excel Sheet Column Number

LeetCode-171

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 = "AB"
Output: 28

Example 2:

Input: columnTitle = "ZY"
Output: 701

method

相当于把一个从1开始的26进制数转换成十进制

int titleToNumber(string columnTitle) {
    long res = 0;   // 会溢出
    for (auto c : columnTitle) {
        res = res * 26 + (c - 'A' + 1);
    }
    return res;
}