Leetcode - Excel Sheet Column Number

My code:

public class Solution {
    public int titleToNumber(String s) {
        if (s == null || s.length() == 0)
            return 0;
        int number = 0;
        for (int i = 0; i < s.length(); i++)
            number = number * 26 + s.charAt(i) - 64;
        return number;
    }
}

My test result:

这道题目太简单了，感觉有点侮辱智商。

**
总结： Math
**

Anyway, Good luck, Richardo!

My code:

public class Solution {
    public int titleToNumber(String s) {
        if (s == null || s.length() == 0) {
            return 0;
        }
        
        int base = 1;
        int ret = 0;
        for (int i = s.length() - 1; i >= 0; i--) {
            char curr = s.charAt(i);
            int diff = (int) (curr - 'A') + 1;
            ret += diff * base;
            base *= 26;
        }
        
        return ret;
    }
}

以前的解法竟然看不懂。。。还大言不惭，侮辱智商。。。

是我变笨了吗？

Fuck

我的思想是找规律：
A-Z: 1-26
AA-AZ: 27-52
BA-BZ: 53-78
...
AAA: 703

AAA = 1 * 26 ^ 2 + 1 * 26 ^ 1 + 1 * 26 ^ 0

从这个公式，也可以看出
Excel Sheet Column Title
那么做的原因了。

int offset = (n - 1) % 26;
while (n > 0) {
    ret = ('A' + offset) + ret;
    n = (n - 1) / 26;  // 去掉  k * (26 ^ x), here 1<=k<=26, so n - 1
    col = (n - 1) % 26; // keep finding the offset of next level
}

感觉差不多就这个思路。

Anyway, Good luck, Richardo! -- 09/05/2016

这些天有了新的思路。其实就是一个26进制转换。

AB

'B' * 26 ^ 0 + 'A' * 26 ^ 1
= 2 * 1 + 1 * 26 = 28

然后可以很快的写出代码：

My code:

public class Solution {
    public int titleToNumber(String s) {
        if (s == null || s.length() == 0) {
            return 0;
        }
        
        int base = 1;
        int ret = 0;
        for (int i = s.length() - 1; i >= 0; i--) {
            int offset = (int) (s.charAt(i) - 'A') + 1;
            ret += base * offset;
            base *= 26;
        }
        
        return ret;
    }
}

终于变成了 easy

Anyway, Good luck, Richardo! -- 09/19/2016