New Problem C++ Solution - "Squares of a Sorted Array"

Author: haoel

README.md

@@ -19,7 +19,7 @@ LeetCode
 |981|[Time Based Key-Value Store](https://leetcode.com/problems/time-based-key-value-store/) | [C++](./algorithms/cpp/timeBasedKeyValueStore/TimeBasedKeyValueStore.cpp)|Medium|
 |980|[Unique Paths III](https://leetcode.com/problems/unique-paths-iii/) | [C++](./algorithms/cpp/uniquePaths/UniquePaths.III.cpp)|Hard|
 |978|[Longest Turbulent Subarray](https://leetcode.com/problems/longest-turbulent-subarray/) | [C++](./algorithms/cpp/longestTurbulentSubarray/LongestTurbulentSubarray.cpp),[Python](./algorithms/python/LongestTurbulentSubarray/maxTurbulenceSize.py)|Medium|
-|977|[Squares of a Sorted Array](https://leetcode.com/problems/squares-of-a-sorted-array/) | [Python](./algorithms/python/SquaresOfSortedArray/sortedSquares.py)|Easy|
+|977|[Squares of a Sorted Array](https://leetcode.com/problems/squares-of-a-sorted-array/) | [C++](./algorithms/cpp/squaresOfASortedArray/SquaresOfASortedArray.cpp), [Python](./algorithms/python/SquaresOfSortedArray/sortedSquares.py)|Easy|
 |976|[Largest Perimeter Triangle](https://leetcode.com/problems/largest-perimeter-triangle/) | [Python](./algorithms/python/LargestPerimeterTriangle/largestPerimeter.py)|Easy|
 |971|[Flip Binary Tree To Match Preorder Traversal](https://leetcode.com/problems/flip-binary-tree-to-match-preorder-traversal/) | [Python](./algorithms/python/FlipBinaryTreeToMatchPreorderTraversal/flipMatchVoyage.py)|Medium|
 |969|[Pancake Sorting](https://leetcode.com/problems/pancake-sorting/) | [Python](./algorithms/python/PancakeSorting/pancakeSort.py)|Medium|

algorithms/cpp/squaresOfASortedArray/SquaresOfASortedArray.cpp

@@ -0,0 +1,65 @@
+// Source : https://leetcode.com/problems/squares-of-a-sorted-array/
+// Author : Hao Chen
+// Date   : 2019-03-26
+
+/***************************************************************************************************** 
+ *
+ * Given an array of integers A sorted in non-decreasing order, return an array of the squares of each 
+ * number, also in sorted non-decreasing order.
+ * 
+ * Example 1:
+ * 
+ * Input: [-4,-1,0,3,10]
+ * Output: [0,1,9,16,100]
+ * 
+ * Example 2:
+ * 
+ * Input: [-7,-3,2,3,11]
+ * Output: [4,9,9,49,121]
+ * 
+ * Note:
+ * 
+ * 	1 <= A.length <= 10000
+ * 	-10000 <= A[i] <= 10000
+ * 	A is sorted in non-decreasing order.
+ * 
+ ******************************************************************************************************/
+
+class Solution {
+public:
+    vector<int> sortedSquares(vector<int>& A) {
+        // find the place, negative numbers are right, positive number are right.
+        // two pointer, one goes left, another goes right.
+
+        //using binary search algorithm
+        const int len = A.size();
+        int low = 0, high = len- 1;
+        int mid =0;
+        while (low <= high) {
+            mid = low + (high - low)/2;
+            if (A[mid] >= 0 ) high = mid - 1;
+            if (A[mid] < 0 ) low = mid + 1;
+        }
+
+        //TRICKY: make sure  A[mid] <= 0 or A[mid] is A[0]
+        if (A[mid] > 0 && mid > 0 ) mid--;
+        //cout << mid << " - "<< A[mid]<<  endl;
+
+        vector<int> result;
+        low = mid; high = mid+1;
+        while ( low >=0 && high < len ) {
+            if ( abs(A[low]) < abs(A[high]) ) {
+                result.push_back(A[low] * A[low]);
+                low --;
+            }else {
+                result.push_back(A[high] * A[high]);
+                high++;
+            }
+        }
+
+        for (;low >= 0; low--) result.push_back(A[low] * A[low]);
+        for (;high<len; high++) result.push_back(A[high] * A[high] );
+
+        return result;
+    }
+};