Merge pull request #31 from raginiisingh/Combination_sum_leetcode

Q39, Combination Sum using Java

leetCode Solutions/Q39_CombinationSum/Q39_CombinationSum.java

@@ -0,0 +1,24 @@
+/* This solution uses the concept of recursion by considering both the cases of idea of picking or not picking an element in the array to find the target sum */
+
+class Solution {
+    public List<List<Integer>> combinationSum(int[] candidates, int target) {
+        List<List<Integer>> result = new ArrayList<>();
+        findCombination(0,candidates,result, new ArrayList<>(), target);
+        return result;
+    }
+    public void findCombination(int i, int arr[],List<List<Integer>> result, ArrayList<Integer> al,int target)     {
+        if(i== arr.length){
+            if(target == 0) result.add(new ArrayList<>(al));
+            return;
+        }
+        if(arr[i]<=target){     
+            //pick single element multiple times
+            al.add(arr[i]);     
+            //we are not changing index i, because we are picking same element multiple times
+            findCombination(i,arr,result,al, target-arr[i]);
+            al.remove(al.size()-1);
+        }
+		    //moving to next index and start again with pick/not-pick principle
+        findCombination(i+1,arr,result, al, target);
+  }
+}