[LeetCode]--168. Excel Sheet Column Title

Given a positive integer, return its corresponding column title as appear in an Excel sheet.

For example:

1 -> A
2 -> B
3 -> C
...
26 -> Z
27 -> AA
28 -> AB 

Credits:
Special thanks to @ifanchu for adding this problem and creating all test cases.

本质上就是将一个10进制数转换为一个26进制的数

注意：由于下标从1开始而不是从0开始，因此要减一操作。

The Best Answer:

/**
     * 最好的方式
     */
    public String convertToTitle2(int n) {
        String ret = "";
        while (n != 0) {
            ret = (char) ((n - 1) % 26 + 'A') + ret;
            n = (n - 1) / 26;
        }
        return ret;
    }

再提供一种递归一种非递归的方式，都是Accept！

递归形式：

/**
     * 递归形式
     * 
     * @param n
     * @return
     */
    public String convertToTitle(int n) {
        if (n == 0)
            return "";
        if (n <= 26)
            return intToStr(n);
        String str = "";
        int temp = n % 26;
        int i = n / 26;
        if (temp == 0)
            i--;
        str += convertToTitle(i);
        str += intToStr(temp);
        return str;
    }

    public String intToStr2(int x) {
        switch (x) {
        case 0:
            return "A";
        case 1:
            return "B";
        case 2:
            return "C";
        case 3:
            return "D";
        case 4:
            return "E";
        case 5:
            return "F";
        case 6:
            return "G";
        case 7:
            return "H";
        case 8:
            return "I";
        case 9:
            return "J";
        case 10:
            return "K";
        case 11:
            return "L";
        case 12:
            return "M";
        case 13:
            return "N";
        case 14:
            return "O";
        case 15:
            return "P";
        case 16:
            return "Q";
        case 17:
            return "R";
        case 18:
            return "S";
        case 19:
            return "T";
        case 20:
            return "U";
        case 21:
            return "V";
        case 22:
            return "W";
        case 23:
            return "X";
        case 24:
            return "Y";
        case 25:
            return "Z";
        }
        return "";
    }

非递归形式：

/**
     * 非递归形式
     * 
     * @param n
     * @return
     */
    public String convertToTitle1(int n) {
        if (n == 0)
            return "";
        if (n <= 26)
            return intToStr(n);
        String str = "";
        int temp = 0;
        while (n != 0) {
            temp = (n - 1) % 26;
            str = intToStr2(temp) + str;
            n = (n - 1) / 26;
        }
        return str;
    }

public String intToStr2(int x) {
        switch (x) {
        case 0:
            return "A";
        case 1:
            return "B";
        case 2:
            return "C";
        case 3:
            return "D";
        case 4:
            return "E";
        case 5:
            return "F";
        case 6:
            return "G";
        case 7:
            return "H";
        case 8:
            return "I";
        case 9:
            return "J";
        case 10:
            return "K";
        case 11:
            return "L";
        case 12:
            return "M";
        case 13:
            return "N";
        case 14:
            return "O";
        case 15:
            return "P";
        case 16:
            return "Q";
        case 17:
            return "R";
        case 18:
            return "S";
        case 19:
            return "T";
        case 20:
            return "U";
        case 21:
            return "V";
        case 22:
            return "W";
        case 23:
            return "X";
        case 24:
            return "Y";
        case 25:
            return "Z";
        }
        return "";
    }

自然没有第一种解决巧妙，直接用余数+’A’，这样就可以直接得出需要的结果字符，而不需要用数组或者这种长长的switch语句。