Add C++ Solutions (#92)

* Create _461.cpp

* refactor 461

* Create _15.cpp

* Create _4.cpp

* Update README.md

added c++ solution for 4 and 15

* Create _3.cpp

* Create _7.cpp

* refactor readme

Add C++ solutions for 3 and 7

* refactor 3.cpp

Author: Anshul1507

Diff for: README.md

@@ -978,11 +978,11 @@ _If you like this project, please leave me a star._ ★
 |10|[Regular Expression Matching](https://leetcode.com/problems/regular-expression-matching/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_10.java)||Hard|DP
 |9|[Palindrome Number](https://leetcode.com/problems/palindrome-number/)|[Java](../master/src/main/java/com/fishercoder/solutions/_9.java), [C++](../master/cpp/_9.cpp)| | Easy
 |8|[String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_8.java)|  |Medium
-|7|[Reverse Integer](https://leetcode.com/problems/reverse-integer/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_7.java) | [:tv:](https://youtu.be/tm1Yrb_SfBM) |Easy | 
+|7|[Reverse Integer](https://leetcode.com/problems/reverse-integer/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_7.java), [C++](../master/cpp/_7.cpp) | [:tv:](https://youtu.be/tm1Yrb_SfBM) |Easy | 
 |6|[ZigZag Conversion](https://leetcode.com/problems/zigzag-conversion/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_6.java) | |Easy | 
 |5|[Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_5.java) | |Medium|
 |4|[Median of Two Sorted Arrays](https://leetcode.com/problems/median-of-two-sorted-arrays/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_4.java), [C++](../master/cpp/_4.cpp) | |Hard | Divide and Conquer
-|3|[Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_3.java) |  |Medium | HashMap, Sliding Window
+|3|[Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_3.java), [C++](../master/cpp/_3.cpp) |  |Medium | HashMap, Sliding Window
 |2|[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_2.java) | |Medium | LinkedList
 |1|[Two Sum](https://leetcode.com/problems/two-sum/)|[Java](../master/src/main/java/com/fishercoder/solutions/_1.java), [C++](../master/cpp/_1.cpp), [Javascript](../master/javascript/_1.js)|[:tv:](https://www.youtube.com/watch?v=kPXOr6pW8KM&t=)|Easy| HashMap 
 

Diff for: cpp/_3.cpp

@@ -0,0 +1,61 @@
+//Solution 1: Using Array Frequency Method
+
+class Solution {
+public:
+    int lengthOfLongestSubstring(string s) {
+        
+        if(s.find_first_not_of(' ') != string::npos){
+            // There's a non-space && visit array ~ 127 ascii chars.
+            int visit[150];
+            memset(visit,0,sizeof(visit));
+            
+            int mx=0,x=0;
+            for(int i=0;i<s.size();i++){
+                if(visit[s[i]]==0){
+                    visit[s[i]]++;
+                    x++;
+                }else{
+                    mx = max(mx,x);
+                    //back to (i-x) index for relooping from the double occurance
+                    if(x>0) i-=x;
+                    x=0;
+                    memset(visit,0,sizeof(visit));
+                }
+            }
+            mx = max(x,mx);
+            return mx;
+        }else{
+            // There's a only white-spaces.
+            if(s.size()>0) return 1;
+            else return 0;
+        }
+        
+    }
+};
+
+//Solutio 2: Using Map Method (High Memory and Time)
+
+class Solution {
+public:
+    int lengthOfLongestSubstring(string s) {
+    
+        unordered_map <char,int> ump;
+            
+        int mx=0,x=0;
+        for(int i=0;i<s.size();i++){
+            if(ump[s[i]]==0){
+                ump[s[i]]++;
+                x++;
+            }else{
+                mx = max(mx,x);
+                //back to (i-x) index for relooping from the double occurance
+                if(x>0) i-=x;
+                x=0;
+                ump.clear();
+            }
+        }
+        mx = max(x,mx);
+        return mx;
+        
+    }
+};

Diff for: cpp/_7.cpp

@@ -0,0 +1,41 @@
+//Faster than 100% submissions
+
+class Solution {
+public:
+    int reverse(int x) {
+        
+        long int res = 0;
+        
+        bool isMinus = false;
+        //To add the minus sign if any negative number
+        if(x<0){
+            isMinus = true;
+        }
+        
+        //convert into positive number
+        x = abs(x);
+        
+        //Function to reverse number
+        while(x>0){
+            int last = x%10;
+            res = res*10 + last;
+            x/=10;
+        }
+        
+        //Adding minus sign in the result
+        if(isMinus){
+            res *= -1;
+        }
+        //Range of int
+        int mn = -2147483648, mx =  2147483647;
+        
+        //Checking if is in range of int
+        if(res > mn and res < mx){
+            res = res;
+        }else{
+            res = 0;
+        }
+        
+        return res;
+    }
+};