add 387 folder & cpp

Author: zouwx2cs

solution/387.First Unique Character in a String/Solution.cpp

@@ -0,0 +1,23 @@
+class Solution {
+public:
+    int firstUniqChar(string s) {
+        vector<int> cnts(26, 0), pos(26, s.size()) ;
+        
+        
+        for (int i = s.size()-1; i >= 0; --i)
+        {
+            int index = s[i] - 'a' ;
+            cnts[index]++ ;
+            pos[index] = i ;
+        }
+        
+        int p = s.size() ;
+        for (int i = 0; i < 26; ++i)
+        {
+            if (cnts[i] == 1 && pos[i] < p)
+                p = pos[i] ;
+        }
+        
+        return p != s.size()? p: -1 ;
+    }
+};