combination sum solved

Author: mintheon

combination-sum/mintheon.java

@@ -0,0 +1,38 @@
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.Deque;
+import java.util.List;
+
+class Solution {
+  /**
+   시간복잡도: O(2^n)
+   공간복잡도: O(n)
+   */
+  public List<List<Integer>> combinationSum(int[] candidates, int target) {
+    List<List<Integer>> answer = new ArrayList<>();
+    Deque<Integer> nums = new ArrayDeque<>();
+
+    backtracking(candidates, answer, nums, target, 0, 0);
+
+    return answer;
+  }
+
+  protected void backtracking(int[] candidates, List<List<Integer>> answer, Deque<Integer> nums, int target, int start, int total) {
+    if(total > target) {
+      return;
+    }
+
+    if (total == target) {
+      answer.add(new ArrayList<>(nums));
+      return;
+    }
+
+    for(int i = start; i < candidates.length; i++) {
+      int num = candidates[i];
+      nums.push(num);
+
+      backtracking(candidates, answer, nums, target, i, total + num);
+      nums.pop();
+    }
+  }
+}