Add BackTrackingTest

src/test/java/BackTrackingTest.java

@@ -0,0 +1,36 @@
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+
+public class BackTrackingTest {
+
+    /*
+     * https://leetcode.com/problems/combination-sum/
+     */
+    @Test
+    void combinationSum() {
+        int[] candidates = {2, 3, 6, 7};
+        int target = 7;
+
+        List<List<Integer>> result = new ArrayList<>();
+        LinkedList<Integer> combination = new LinkedList<>();
+        backtrack(candidates, target, combination, 0, result);
+        System.out.println("result = " + result);
+    }
+
+    void backtrack(int[] candidates, int remain, LinkedList<Integer> combination, int start, List<List<Integer>> result) {
+        if (remain == 0) {
+            result.add(new ArrayList<>(combination));
+        } else if (remain < 0) {
+            return;
+        }
+
+        for (int i = start; i < candidates.length; i++) {
+            combination.add(candidates[i]);
+            backtrack(candidates, remain - candidates[i], combination, i, result);
+            combination.removeLast();
+        }
+    }
+}