feat: combination sum

Author: minji-go

combination-sum/minji-go.java

@@ -0,0 +1,33 @@
+/*
+    Problem: https://leetcode.com/problems/combination-sum/
+    Description: return a list of all unique combinations of candidates where the chosen numbers sum to target
+    Concept: Array, Backtracking
+    Time Complexity: O(Nⁿ), Runtime 2ms
+    Space Complexity: O(N), Memory 44.88MB
+
+    - Time Complexity, Space Complexity를 어떻게 계산해야할지 어렵네요 :(
+*/
+class Solution {
+    public List<List<Integer>> answer = new ArrayList<>();
+
+    public List<List<Integer>> combinationSum(int[] candidates, int target) {
+        Arrays.sort(candidates);
+        findCombination(candidates, target, new ArrayList<>(), 0);
+        return answer;
+    }
+
+    public void findCombination(int[] candidates, int target, List<Integer> combination, int idx) {
+        if(target == 0) {
+            answer.add(new ArrayList<>(combination));
+            return;
+        }
+
+        for(int i=idx; i<candidates.length; i++) {
+            if(candidates[i] > target) break;
+
+            combination.add(candidates[i]);
+            findCombination(candidates, target-candidates[i], combination, i);
+            combination.remove(combination.size()-1);
+        }
+    }
+}