Code refactor

Author: gouthampradhan

problems/src/BTfromPreorder.java

@@ -1,10 +1,19 @@
+package array;
+
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 
 /**
  * Created by gouthamvidyapradhan on 25/03/2017.
- * Accepted
+ *
+ * Given an index k, return the kth row of the Pascal's triangle.
+
+ For example, given k = 3,
+ Return [1,3,3,1].
+
+ Note:
+ Could you optimize your algorithm to use only O(k) extra space?
  */
 public class PascalsTriangle
 {

problems/src/GrayCode.java

@@ -0,0 +1,42 @@
+package array;
+
+/**
+ Created by gouthamvidyapradhan on 04/05/2017.
+
+ Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].
+
+ Solve it without division and in O(n).
+
+ For example, given [1,2,3,4], return [24,12,8,6].
+
+ Follow up:
+ Could you solve it with constant space complexity? (Note: The output array does not count as extra space for the purpose of space complexity analysis.)
+ */
+
+public class ProductOfArrayExceptSelf
+{
+    public static void main(String[] args)
+    {
+        int[] nums = {1,2,3,4};
+        int[] result = new ProductOfArrayExceptSelf().productExceptSelf(nums);
+        for (int r : result)
+            System.out.print(r + " ");
+    }
+
+    public int[] productExceptSelf(int[] nums)
+    {
+        int[] result = new int[nums.length];
+        for(int i = 0, temp = 1, l = nums.length; i < l; i++)
+        {
+            result[i] = temp;
+            temp *= nums[i];
+        }
+        for(int i = nums.length - 1, temp = 1; i >= 0; i--)
+        {
+            result[i] = result[i] * temp;
+            temp *= nums[i];
+        }
+        return result;
+    }
+
+}

problems/src/LowestCommonAncestor.java

@@ -1,6 +1,13 @@
+package array;
+
 /**
  * Created by gouthamvidyapradhan on 21/03/2017.
- * Accepted
+ * You are given an n x n 2D matrix representing an image.
+
+ Rotate the image by 90 degrees (clockwise).
+
+ Follow up:
+ Could you do this in-place?
  */
 public class RotateMatrix
 {

problems/src/MedianOfTwoSortedArrays.java

@@ -1,9 +1,19 @@
+package array;
+
 import java.util.HashSet;
 import java.util.Set;
 
 /**
  * Created by pradhang on 3/28/2017.
- * Accepted
+ * Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.
+
+ click to show follow up.
+
+ Follow up:
+ Did you use extra space?
+ A straight forward solution using O(mn) space is probably a bad idea.
+ A simple improvement uses O(m + n) space, but still not the best solution.
+ Could you devise a constant space solution?
  */
 public class SetMatrixZeroes
 {