Added solution for Spiral-matrix in cpp (#205)

* Create Spiral-matrix.cpp

* Update README.md

Author: Nikhil-1503

C++/Spiral-matrix.cpp

@@ -0,0 +1,37 @@
+//Problem Number : 54
+//Problem Name : Spiral Matrix
+//Problem Statement : Given an m x n matrix, return all elements of the matrix in spiral order.
+
+class Solution {
+public:
+    vector<int> spiralOrder(vector<vector<int>>& matrix) {
+        vector<int>res;
+        int left = 0, top = 0, down = matrix.size()-1, right = matrix[0].size()-1;
+        
+        while(left <= right && top <= down){            
+            //From left to right on top side
+            for(int i = left; i <= right; i++)
+                res.push_back(matrix[top][i]);
+            top++;
+            //From top to down on right side
+            for(int i = top; i <= down; i++)
+                res.push_back(matrix[i][right]);
+            right--;
+            if(top <= down){
+            //From right to left on down side
+                for(int i = right; i >= left; i--)
+                    res.push_back(matrix[down][i]);
+                down--;
+            }
+            if(left <= right){
+            //From down to top on left side
+                for(int i = down; i >= top; i--)
+                    res.push_back(matrix[i][left]);
+                left++;
+            }
+        }
+        return res;
+    }
+};
+
+//This code is contributed by Nikhil-1503

README.md

@@ -145,6 +145,8 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 36      | [Valid Sudoku](https://leetcode.com/problems/valid-sudoku/)                                                                   | [Java](./Java/valid-sudoku.java)                                                                                  | O(N^2)       | O(N)          | Medium     | Array, 2D Matrix   |
 | 1512    | [Number of Good Pairs](https://leetcode.com/problems/number-of-good-pairs/)                                                   | [Java](./Java/Number-of-Good-Pairs.java)                                                                          | O(N^2)       | O(1)          | Easy       | Array              |
 | 162     | [Find Peak element](https://leetcode.com/problems/find-peak-element/)                                                         | [javascript](https://github.com/codedecks-in/LeetCode-Solutions/blob/master/JavaScript/findPeakElement.js)                                                                     | o(Logn)      | O(1)          | Medium     | Array              |
+| 54     | [Spiral Matrix](https://leetcode.com/problems/spiral-matrix/)                                                         | [C++](./C++/Spiral-matrix.cpp)                                                                     | O(M\*N)      | O(M\*N)         | Medium     | Array              |
+
 
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