Added C++ Solution (#112)

* Added C++ solution 

31. Next Permutation C++ solution

* Update README.md

* Update _31.cpp

Author: Anshul1507

README.md

@@ -990,7 +990,7 @@ _If you like this project, please leave me a star._ ★
 |34|[Search for a Range](https://leetcode.com/problems/search-for-a-range/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_34.java)||Medium|Array, Binary Search
 |33|[Search in Rotated Sorted Array](https://leetcode.com/problems/search-in-rotated-sorted-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_33.java)||Medium|Binary Search
 |32|[Longest Valid Parentheses](https://leetcode.com/problems/longest-valid-parentheses/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_32.java)||Hard|Stack, DP
-|31|[Next Permutation](https://leetcode.com/problems/parents-permutation)|[Solution](../master/src/main/java/com/fishercoder/solutions/_31.java)||Medium|Array
+|31|[Next Permutation](https://leetcode.com/problems/parents-permutation)|[Solution](../master/src/main/java/com/fishercoder/solutions/_31.java), [C++](../master/cpp/_31.cpp)||Medium|Array
 |30|[Substring with Concatenation of All Words](https://leetcode.com/problems/substring-with-concatenation-of-all-words/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_30.java)||Hard| HashMap
 |29|[Divide Two Integers](https://leetcode.com/problems/divide-two-integers/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_29.java)||Medium|
 |28|[Implement strStr()](https://leetcode.com/problems/implement-strstr/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_28.java)||Easy| String

cpp/_31.cpp

@@ -0,0 +1,33 @@
+class Solution {
+public:
+    void nextPermutation(vector<int>& nums) {
+    
+        int i1;
+        int i2;
+        bool hasPermutation = false;
+        
+        for(int i=nums.size()-1; i>0; i--){
+            if(nums[i-1]<nums[i]){
+                i1 = i-1;
+                i2 = i;
+                hasPermutation = true;
+                break;
+            }
+        }
+        
+        if(hasPermutation){
+            int j=i2;
+            for(int i=nums.size()-1; i>i1; i--){
+                if(nums[i]>nums[i1]){
+                    j=i;
+                    break;
+                }
+            }
+            swap(nums[i1], nums[j]);
+            reverse(nums.begin()+i1+1, nums.end());
+        }else{
+            sort(nums.begin(), nums.end());
+        }
+  
+    }
+};