Create Return subsets sum to K

Author: akshayavb99

Course 2 - Data Structures in JAVA/Lecture 17 - Recursion III/Return subsets sum to K

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+/*
+Given an array A of size n and an integer K, return all subsets of A which sum to K.
+Subsets are of length varying from 0 to n, that contain elements of the array. But the order of elements should remain same as in the input array.
+Note : The order of subsets are not important.
+
+Input format :
+Line 1 : Integer n, Size of input array
+Line 2 : Array elements separated by space
+Line 3 : K 
+
+Constraints :
+1 <= n <= 20
+
+Sample Input :
+9 
+5 12 3 17 1 18 15 3 17 
+6
+Sample Output :
+3 3
+5 1
+*/
+
+
+public class solution {
+
+	// Return a 2D array that contains all the subsets which sum to k
+	public static int[][] subsetsSumK(int input[], int k) {
+		// Write your code here
+        return subsetsSumKHelper(input,k,0);
+	}
+    
+    private static int[][] subsetsSumKHelper(int input[], int k, int startIndex)
+    {
+        //Base case - If startIndex == input.length
+        //We can have two cases in the base condition
+        //1. If k==0 - This means the desired sum has been achieved by including the last element of the input array
+        //2. If k!=0 - Desired sum has not been achieved even when last element is included
+        if (startIndex==input.length)
+        {
+            int arr[][];
+            if (k==0)
+            {
+                 arr = new int[1][0];
+            }
+            else
+            {
+                arr = new int[0][0];
+            }
+            return arr;
+        }
+        
+        //Considering recursive hypothesis where we have the subsets of two cases
+        //1. Subsets containing current input[startIndex] element - temp1
+        //2. Subsets not containing current input[startIndex] element - temp2
+        int temp1[][] = subsetsSumKHelper(input,k-input[startIndex],startIndex+1);
+        int temp2[][] = subsetsSumKHelper(input,k,startIndex+1);
+        
+        //Now, we simply need to combine temp1 and temp2 and return to the calling function
+        //When copying temp1 into output, we need to ensure we also include current input[startIndex] as the first element of that row
+        int output[][] = new int[temp1.length+temp2.length][];
+        for (int i=0;i<temp2.length;i++)
+        {
+            output[i] = new int[temp2[i].length];
+            for (int j=0;j<temp2[i].length;j++)
+            {
+                output[i][j]=temp2[i][j];
+            }
+        } 
+        
+        for (int i=0;i<temp1.length;i++)
+        {
+            output[i+temp2.length] = new int[temp1[i].length+1];
+            output[i+temp2.length][0] = input[startIndex];
+            for (int j=1;j<output[i+temp2.length].length;j++)
+            {
+                output[i+temp2.length][j]=temp1[i][j-1];
+            }
+        }
+        
+        return output;
+    }
+}