171.Excel Sheet Column Number

Description

这里记录进制问题集合，非常简单，长期更新

1. Related to question Excel Sheet Column Title
   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
2. 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

Solution

[leetcode 171] Excel Sheet Column Number

很简单，就当成进制问题就可以了，然后一个递归就解决了：

public int titleToNumber(String s) {
    int n=s.length();
    int res=0;
    return getNumber(n,s);
}

private int getNumber(int n, String s) {
    if(n==0)return 0;
    return (int)((s.charAt(0)-'A'+1)*Math.pow(26,n-1)+getNumber(n-1,s.substring(1)));
}

[leetcode 168] Excel Sheet Column Title

也是递归问题，将大问题转小问题，这里取余的时候需要考虑除数的问题(26的问题)

public String convertToTitle(int n) {
        String res="";
        return getColumn(res,n);
    }

private String getColumn(String res, int n) {
        if(n==0)return res;
        if(n%26==0){res='Z'+res;n=n/26-1;}
        else {res=(char)('A'+n%26-1)+res;n=n/26;}
        res=getColumn(res,n);
        return res;
    }