add: CombinationsOfSumK

Author: Jer3myYu

java/Backtracking/CombinationsOfSumK.java

@@ -0,0 +1,33 @@
+import java.util.ArrayList;
+import java.util.List;
+
+public class CombinationsOfSumK {
+    public List<List<Integer>> combinationsOfSumK(int[] nums, int target) {
+        List<List<Integer>> result = new ArrayList<>();
+        dfs(new ArrayList<>(), 0, nums, target, result);
+        return result;
+    }
+
+    private void dfs(List<Integer> combination, int startIndex, int[] nums, int target, List<List<Integer>> result) {
+        // Termination condition: If the target is equal to 0, we found a combination 
+        // that sums to 'k'.
+        if (target == 0) {
+            result.add(new ArrayList<>(combination));
+            return;
+        }
+        // Termination condition: If the target is less than 0, no more valid 
+        // combinations can be created by adding it to the current combination.
+        if (target < 0) {
+            return;
+        }
+        // Starting from start_index, explore all combinations after adding nums[i].
+        for (int i = startIndex; i < nums.length; i++) {
+            // Add the current number to create a new combination.
+            combination.add(nums[i]);
+            // Recursively explore all paths that branch from this new combination.
+            dfs(combination, i, nums, target - nums[i], result);
+            // Backtrack by removing the number we just added.
+            combination.remove(combination.size() - 1);
+        }
+    }
+}