LeetCode.158(171) Excel Sheet Column Title&Excel Sheet Column Number

题目158：

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 

分析：

class Solution {    public String convertToTitle(int n) {        //给定整数，求其Excel表达        String res="";        while(n>0){            n--;            char c=(char)('A'+n%26);            res=String.valueOf(c)+res;            n/=26;        }        return res;    }}

题目171:

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 

class Solution {    public int titleToNumber(String s) {        //给定字符串，给出其整数表达        //类型于26进制(注意对应字母所在位置，需要加上其后面位数*25)        char [] ch=s.toCharArray();        int sum=0;        for(int i=0;i<ch.length;i++){            int temp=ch[i]-'A'+1;            sum+=temp*Math.pow(26,ch.length-1-i);        }        return sum;    }    }