added c++ solution for 1st in queue

Queue/C++/1.First_Unique_Character_In_String.cpp

@@ -0,0 +1,78 @@
+/*
+-> Problem Statement
+- Find First no-repeating characher in given string and return its index. If does not exist return -1.
+
+-> Approach Explanation:
+- First traverse the string, save frequency of each character in array and push indexes of elements in queue when frequency of character becomes one.
+- Now pop indexes from queue having character frequency > 1 
+- If non-repeating character will be there then queue's first element would be that character, return it or -1 if queue is empty
+*/
+
+#include <iostream>
+#include <cstring>
+#include <queue>
+using namespace std;
+
+class Solution {
+public:
+    int firstUniqChar(string s) {
+
+        int freq[26];
+        queue<int>q;
+        memset(freq,0,sizeof(freq));               
+
+        for(int i=0;i<s.size();i++)
+        {                                                          
+            if(++freq[s[i]-'a'] == 1)                      // saving frequency of lowercase letters 
+                q.push(i);                                  // pushing indexes when frequency becomes one to maintain order of characters
+
+        }                               
+        while(!q.empty() && freq[s[q.front()]-'a'] > 1)    // poping front indexes till frequency of its element is > 1 and queue is not empty 
+            q.pop();
+
+        return !q.empty() ? q.front() : -1;                // returning first index from q's front if queue is not empty else -1
+    }
+};
+
+int main() 
+{
+    cout<<"\nEnter number of test cases/strings you have to check: ";
+	int t; cin>>t;  //no. of test cases
+
+	/*
+	Constraints:
+    1 <= string's length <= 10^5
+    string consists of only lowercase English letters.
+    */
+
+	while (t--)
+	{
+	    cout<<"\n\nEnter String ( Input ): ";
+	    string s; cin >> s;
+
+	    Solution *ob;
+        cout<<"First non-repeating index in string is  :";
+	    cout <<  ob-> firstUniqChar(s);
+
+	}
+	return 0;
+}
+
+/*
+SAMPLE INPUT
+3				         // number of test cases / strings
+leetcode				 // string for test case:1 	             
+codeforces				 // string for test case:2 	   
+lgmsocletsgrowmore         // integers array / vector for test case:2
+ 
+SAMPLE OUTPUT (excluding interactive instructions)
+0  ( index 0 for non-repeating 'l' )
+2  ( index 2 for non-repeating 'd' )
+5  ( index 5 for non-repeating 'c' )
+
+COMPLEXITY ANALYSIS : N= no.of characters in string
+Time : O(N) to iterate string and maximum O(N) to traverse and pop from queue. 
+       Hence, O(N) overall.
+Space: O(1) for stringinput and aux space: O(1) for fixed max size 26 of array or queue.
+       Hence, O(1) overall.
+*/