LeetCode171. Excel Sheet Column Number

一、题目

Given a string columnTitle that represents the column title as appears 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

Constraints:

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

二、题解

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--){
            int k = columnTitle[i] - 'A' + 1;
            res += k * mul;
            mul *= 26;
        }
        return res;
    }
};
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