LeetCode 171. Excel Sheet Column Number

原题链接在这里：https://leetcode.com/problems/excel-sheet-column-number/

题目：

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 
    ...

Example 1:

Input: "A"
Output: 1

Example 2:

Input: "AB"
Output: 28

Example 3:

Input: "ZY"
Output: 701

题解：

Keep accumlating.

Time O(n). n = s.length().

Space O(1).

AC Java:

public class Solution {
    public int titleToNumber(String s) {
        if(s == null || s.length() == 0){
            throw new IllegalArgumentException("Invalid input string.");
        }
        int res = 0;
        for(int i = 0; i<s.length(); i++){
            res = res*26 + (int)(s.charAt(i)-'A') + 1;
        }
        return res;
    }
}

类似Excel Sheet Column Title.