39. Combination Sum

Author: TonyKim9401

combination-sum/TonyKim9401.java

@@ -0,0 +1,23 @@
+class Solution {
+    // time complexity: O(2^n);
+    // space complecity: O(n*m);
+    private List<List<Integer>> output = new ArrayList<>();
+    public List<List<Integer>> combinationSum(int[] candidates, int target) {
+        backtracking(candidates, 0, target, new ArrayList<>());
+        return output;
+    }
+
+    public void backtracking(int[] candidates, int idx, int target, List<Integer> inside) {
+        if (target == 0) {
+            output.add(new ArrayList<>(inside));
+            return;
+        }
+
+        if (idx > candidates.length - 1 || target < 0) return;
+
+        inside.add(candidates[idx]);
+        backtracking(candidates, idx, target - candidates[idx], inside);
+        inside.remove(inside.size()-1);
+        backtracking(candidates, idx+1, target, inside);
+    }
+}