New Problem "First Unique Character in a String"

README.md

@@ -8,6 +8,7 @@ LeetCode
 
 | # | Title | Solution | Difficulty |
 |---| ----- | -------- | ---------- |
+|387|[First Unique Character in a String](https://leetcode.com/problems/first-unique-character-in-a-string/) | [C++](./algorithms/cpp/firstUniqueCharacterInAString/FirstUniqueCharacterInAString.cpp)|Easy|
 |386|[Lexicographical Numbers](https://leetcode.com/problems/lexicographical-numbers/) | [C++](./algorithms/cpp/lexicographicalNumbers/LexicographicalNumbers.cpp)|Medium|
 |377|[Combination Sum IV](https://leetcode.com/problems/combination-sum-iv/) | [C++](./algorithms/cpp/combinationSumIV/combinationSumIV.cpp)|Medium|
 |376|[Wiggle Subsequence](https://leetcode.com/problems/wiggle-subsequence/) | [C++](./algorithms/cpp/wiggleSubsequence/wiggleSubsequence.cpp)|Medium|

algorithms/cpp/firstUniqueCharacterInAString/FirstUniqueCharacterInAString.cpp

@@ -0,0 +1,55 @@
+// Source : https://leetcode.com/problems/first-unique-character-in-a-string/
+// Author : Hao Chen
+// Date   : 2016-08-23
+
+/*************************************************************************************** 
+ *
+ * Given a string, find the first non-repeating character in it and return it's index. 
+ * If it doesn't exist, return -1.
+ * 
+ * Examples:
+ * 
+ * s = "leetcode"
+ * return 0.
+ * 
+ * s = "loveleetcode",
+ * return 2.
+ * 
+ * Note: You may assume the string contain only lowercase letters.
+ ***************************************************************************************/
+
+class Solution {
+public:
+    int firstUniqChar(string s) {
+        //As the question mentioned, there only have lower case chars, 
+        //so the MAX_CHAR can be defined as 26, but I want this algorithm be more general for all ASCII
+        #define MAX_CHAR 256
+        #define NOT_FOUND  -1
+        #define DUPLICATION -2
+        
+        // initlize all chars status to NOT_FOUND
+        int pos_map[MAX_CHAR];
+        memset(pos_map, NOT_FOUND,sizeof(pos_map));
+        
+        // if it is the first time to find, set the status to its postion
+        // if it is the second time to find, set the status to duplication
+        // if it has already duplicated, do nothing 
+        for (int i=0; i<s.size(); i++){
+            if ( pos_map[s[i]] >= 0 ) {
+                pos_map[s[i]] = DUPLICATION;
+            }else if ( pos_map[s[i]] == NOT_FOUND ) {
+                pos_map[s[i]] = i;
+            }
+        }
+        
+        // find the lowest postion
+        int pos = INT_MAX;
+        for (auto item : pos_map) {
+            cout << item << ",";
+            if (item >= 0 && item < pos) {
+                pos = item;
+            }
+        }
+        return pos == INT_MAX ? -1 : pos;
+    }
+};