leetcode-171-easy

Excel Sheet Column Number

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"].

思路一：26 进制换算

    public int titleToNumber(String columnTitle) {
        char[] chars = columnTitle.toCharArray();

        int ans = 0;
        int val = 0;
        int j = 0;
        for (int i = chars.length - 1; i >= 0; i--) {
            val = (int) Math.pow(26, j);
            j++;
            ans += (chars[i] - 'A' + 1) * val;
        }

        return ans;
    }