added 189 (#165)

* added 189

* added 189

* Update 189.Rotate array

* added 189

* added 189

Author: ShambhaviSharma0110

C++/189.Rotate-array.cpp

@@ -0,0 +1,32 @@
+difficulty level: Medium
+class Solution {
+public:
+    void rotate(vector<int>& nums, int k) {
+        int n = nums.size();
+        k = k % n;
+        // we first reverse all the elements,[7 6 5 4 3 2 1]
+        for (int i = 0, j = n - 1; i < j; i++, j--) {
+            swap(nums[i], nums[j]);
+        }
+       // then we reverse the set of elements sized k for example [7 6 5 4 3 2 1] = [ 5 6 7 4 3 2 1] 
+        for (int i = 0, j = k - 1; i < j; i++, j--) {
+            swap(nums[i], nums[j]);
+        }
+        //finally we reverse the ending elements too = 5 6 7 1 2 3 4
+        for (int i = k, j = n - 1; i < j; i++, j--) {
+            swap(nums[i], nums[j]);
+        }
+    }
+};
+
+Time complexity:O(n)
+Space Complexity:O(1)
+/*
+Input: nums = [1,2,3,4,5,6,7], k = 3
+Output: [5,6,7,1,2,3,4]
+
+Example 2:
+
+Input: nums = [-1,-100,3,99], k = 2
+Output: [3,99,-1,-100]
+*/