add combinations

Recursion/CombinationOne.java

@@ -0,0 +1,73 @@
+// https://leetcode.com/problems/combination-sum/
+
+import java.util.*;
+
+class CombinationOne {
+
+    public static void findCombination(int currentIndex, List<Integer> ds, int candidates[], int n, int target, List<List<Integer>> finalAnswer){
+
+        if (currentIndex == n){
+            if(target == 0){
+                finalAnswer.add(new ArrayList<>(ds));
+            }
+            return;
+        }
+
+        if (candidates[currentIndex] <= target){
+            ds.add(candidates[currentIndex]);
+
+            // Reuse same element
+            findCombination(currentIndex, ds, candidates, n, target - candidates[currentIndex], finalAnswer);
+
+            ds.remove(ds.size() - 1);
+        }
+
+        // Move to next index
+        findCombination(currentIndex + 1, ds, candidates, n, target, finalAnswer);
+    }
+
+    public List<List<Integer>> combinationSum(int[] candidates, int target) {
+
+        int n = candidates.length;
+
+        List<List<Integer>> finalAnswer = new ArrayList<>();
+        List<Integer> ds = new ArrayList<>();
+
+        findCombination(0, ds, candidates, n, target, finalAnswer);
+
+        return finalAnswer;
+    }
+}
+
+
+public class Main {
+
+    public static void main(String[] args) {
+
+        Scanner sc = new Scanner(System.in);
+
+        System.out.print("Enter number of elements: ");
+        int n = sc.nextInt();
+
+        int[] candidates = new int[n];
+
+        System.out.println("Enter elements:");
+        for(int i = 0; i < n; i++){
+            candidates[i] = sc.nextInt();
+        }
+
+        System.out.print("Enter target: ");
+        int target = sc.nextInt();
+
+        Solution obj = new Solution();
+
+        List<List<Integer>> result = obj.combinationSum(candidates, target);
+
+        System.out.println("Possible combinations are:");
+        for(List<Integer> list : result){
+            System.out.println(list);
+        }
+
+        sc.close();
+    }
+}

Recursion/CombinationTwo.java

@@ -0,0 +1,70 @@
+// https://leetcode.com/problems/combination-sum-ii/
+import java.util.*;
+
+class CombinationTwo {
+
+    public static void findCombination(int currentIndex, List<Integer> ds, int candidates[], int target, List<List<Integer>> finalAnswer){
+        
+        if (target == 0){
+            finalAnswer.add(new ArrayList<>(ds));
+            return;
+        }
+
+        for (int i = currentIndex; i < candidates.length; i++){
+
+            if (i > currentIndex && candidates[i] == candidates[i-1]) continue;
+
+            if (candidates[i] > target) break;
+
+            ds.add(candidates[i]);
+
+            findCombination(i + 1, ds, candidates, target - candidates[i], finalAnswer);
+
+            ds.remove(ds.size() - 1);
+        }
+    }
+
+    public List<List<Integer>> combinationSum2(int[] candidates, int target) {
+
+        Arrays.sort(candidates);
+
+        List<List<Integer>> finalAnswer = new ArrayList<>();
+        List<Integer> ds = new ArrayList<>();
+
+        findCombination(0, ds, candidates, target, finalAnswer);
+
+        return finalAnswer;
+    }
+}
+
+
+public class Main {
+    public static void main(String[] args) {
+
+        Scanner sc = new Scanner(System.in);
+
+        System.out.print("Enter number of elements: ");
+        int n = sc.nextInt();
+
+        int[] candidates = new int[n];
+
+        System.out.println("Enter elements:");
+        for(int i = 0; i < n; i++){
+            candidates[i] = sc.nextInt();
+        }
+
+        System.out.print("Enter target: ");
+        int target = sc.nextInt();
+
+        Solution obj = new Solution();
+
+        List<List<Integer>> result = obj.combinationSum2(candidates, target);
+
+        System.out.println("Unique combinations are:");
+        for(List<Integer> list : result){
+            System.out.println(list);
+        }
+
+        sc.close();
+    }
+}