add digits

Author: jackzhenguo

README.md

@@ -1,48 +1,14 @@
 # `Today Update`
 ## Math
-### 9 Palindrome Number
-*  [Github:#9 Palindrome Number](/Math/Math.Lib/IssPalindromeSln.cs)
-*  [CSDN:#9 Palindrome Number](http://blog.csdn.net/daigualu/article/details/72717009)
-   ```C#
-      public bool IsPalindrome(int x)
-        {
-            int palindromex = 0, tmp = x;
-            int sumbit = 0;
-            //calcuate bit count
-            while (tmp > 0)
-            {
-                sumbit++;
-                tmp /= 10;
-            }
-            tmp = x;
-            //get a number reversely
-            while (tmp > 0)
-            {
-                //if palindromex happens overflow, it would return false;
-                palindromex += tmp % 10 * (int)System.Math.Pow(10, --sumbit);               
-                tmp /= 10;
-            }
-            return palindromex == x;
-        }
-   ```
+### 258 Add Digits
+*  [Github:#258 Add Digits](/Math/Math.Lib/AddDigitsSln.cs)
+*  [CSDN:#258 Add Digits](http://blog.csdn.net/daigualu/article/details/72724479)
+   * Tips:
+     * https://en.wikipedia.org/wiki/Digital_root#Congruence_formula 
+     * https://en.wikipedia.org/wiki/Vedic_square
+   * In Indian mathematics, a Vedic square is a variation on a typical 9 × 9 multiplication table where the entry in each cell is the digital root of the product of the column and row headings i.e. the remainder when the product of the row and column headings is divided by 9 (with remainder 0 represented by 9). Numerous geometric patterns and symmetries can be observed in a Vedic square some of which can be found in traditional Islamic art.   
+    ![VedicSquare](/Math/Math.Lib/VedicSquare.png)
 
-### 171 Excel Sheet Column Number
-*  [Github:#171 Excel Sheet Column Number](/Math/Math.Lib/ExcelColumnNumberSln.cs)
-*  [CSDN:#171 Excel Sheet Column Number](http://blog.csdn.net/daigualu/article/details/72717145)
-  	 ```C#
-	    public int TitleToNumber(string s)
-        {
-            char[] chs= {'A','B','C','D','E','F','G','H','I','J','K',
-            'L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};   
-            Dictionary<char,int> dict = new Dictionary<char,int>();
-            for(int i=0; i<chs.Length;i++) dict.Add(chs[i],i+1);
-            int scnt = s.Length, rtnsum=0;
-            for (int i = scnt - 1,j=0; i >= 0; i--,j++)
-              rtnsum += dict[s[i]] * (int)System.Math.Pow(26, j);
-            return rtnsum;
-        }
-
-	 ```
 ---
 ---
 
@@ -226,7 +192,12 @@ Tags are following:
 *  [CSDN:#69 Sqrt(x)](http://blog.csdn.net/daigualu/article/details/72578272)
    * Tips:
      * careful to prevent overflowing! Again careful to **overflow**!
-
+### 9 Palindrome Number
+*  [Github:#9 Palindrome Number](/Math/Math.Lib/IssPalindromeSln.cs)
+*  [CSDN:#9 Palindrome Number](http://blog.csdn.net/daigualu/article/details/72717009)
+### 171 Excel Sheet Column Number
+*  [Github:#171 Excel Sheet Column Number](/Math/Math.Lib/ExcelColumnNumberSln.cs)
+*  [CSDN:#171 Excel Sheet Column Number](http://blog.csdn.net/daigualu/article/details/72717145)
 ## Two Pointers
 * [#345	Reverse Vowels of a String](http://blog.csdn.net/daigualu/article/details/69257693)