LeetCode-Excel Sheet Column Number

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 

这种题跟实现字符串二进制是一个道理，上三种不同的代码版本

<span style="white-space:pre">		</span>
public int titleToNumber(String s) {
        int result = 0;
		for (int i = 0; i < s.length(); i++) {
			result = result * 26 + s.charAt(i) - 'A' + 1;
		}
		return result;
    }

public int titleToNumber(String s) {
		int result = 0;
		char[] chars = s.toCharArray();
		for (int i = 0; i < chars.length; i++) {
			result += (chars[chars.length - i - 1] - 'A' + 1) * Math.pow(26, i);
		}
		return result;
	}

可以实现一个递归版本的

		public int titleToNumber(String s) {
       		if (s.length() < 1) {
			return 0;
		}
		char c = s.charAt(s.length() - 1);
		return titleToNumber(s.substring(0, s.length()-1)) * 26 + c - 'A' + 1; 
    }