New Problem Solution "Convert a Number to Hexadecimal"

README.md

@@ -8,6 +8,7 @@ LeetCode
 
 | # | Title | Solution | Difficulty |
 |---| ----- | -------- | ---------- |
+|405|[Convert a Number to Hexadecimal](https://leetcode.com/problems/convert-a-number-to-hexadecimal/) | [C++](./algorithms/cpp/convertANumberToHexadecimal/ConvertANumberToHexadecimal.cpp)|Easy|
 |404|[Sum of Left Leaves](https://leetcode.com/problems/sum-of-left-leaves/) | [C++](./algorithms/cpp/sumOfLeftLeaves/SumOfLeftLeaves.cpp)|Easy|
 |402|[Remove K Digits](https://leetcode.com/problems/remove-k-digits/) | [C++](./algorithms/cpp/removeKDigits/RemoveKDigits.cpp)|Medium|
 |401|[Binary Watch](https://leetcode.com/problems/binary-watch/) | [C++](./algorithms/cpp/binaryWatch/BinaryWatch.cpp)|Easy|

algorithms/cpp/convertANumberToHexadecimal/ConvertANumberToHexadecimal.cpp

@@ -0,0 +1,56 @@
+// Source : https://leetcode.com/problems/convert-a-number-to-hexadecimal/
+// Author : Hao Chen
+// Date   : 2016-11-12
+
+/*************************************************************************************** 
+ *
+ * Given an integer, write an algorithm to convert it to hexadecimal. For negative 
+ * integer, two’s complement method is used.
+ * 
+ * Note:
+ * 
+ * All letters in hexadecimal (a-f) must be in lowercase.
+ * The hexadecimal string must not contain extra leading 0s. If the number is zero, it 
+ * is represented by a single zero character '0'; otherwise, the first character in the 
+ * hexadecimal string will not be the zero character.
+ * The given number is guaranteed to fit within the range of a 32-bit signed integer.
+ * You must not use any method provided by the library which converts/formats the 
+ * number to hex directly.
+ * 
+ * Example 1:
+ * 
+ * Input:
+ * 26
+ * 
+ * Output:
+ * "1a"
+ * 
+ * Example 2:
+ * 
+ * Input:
+ * -1
+ * 
+ * Output:
+ * "ffffffff"
+ ***************************************************************************************/
+
+class Solution {
+public:
+
+    string toHex(int num) {
+
+        if (num == 0) return "0";
+
+        unsigned int x = num;
+
+        string result;
+        for(;x > 0; x/=16) {
+            int n = x % 16;
+            char c;
+            if (n < 10) c = n + '0';
+            else c = 'a' + n - 10 ;
+            result = c + result;
+        }
+        return result;
+    }
+};