solution(java): 40. Combination Sum II

40. Combination Sum II
- Java

Medium/40. Combination Sum II/README.md

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+# LeetCode 40. Combination Sum II
+
+## Problem Description
+Given a collection of candidate numbers (`candidates`) and a target number (`target`), find all unique combinations in `candidates` where the candidate numbers sum to `target`.
+
+Each number in `candidates` may only be used once in the combination.
+
+**Note:** The solution set must not contain duplicate combinations.
+
+### Test Cases
+
+**Example 1:**
+
+> **Input:** candidates = [10,1,2,7,6,1,5], target = 8
+> 
+> **Output:**
+>
+> [
+>
+> [1,1,6],
+>
+> [1,2,5],
+>
+> [1,7],
+>
+> [2,6]
+>
+> ]
+
+**Example 2:**
+
+> **Input:** candidates = [2,5,2,1,2], target = 5
+>
+> **Output:**
+>
+> [
+>
+> [1,2,2],
+>
+> [5]
+>
+> ]
+
+### Constraints:
+
+`1 <= candidates.length <= 100`
+
+`1 <= candidates[i] <= 50`
+
+`1 <= target <= 30`
+
+### Link
+
+https://leetcode.com/problems/combination-sum-ii/

Medium/40. Combination Sum II/Solution.java

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+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+class Solution {
+    public List<List<Integer>> combinationSum2(int[] candidates, int target) {
+        List<List<Integer>> result = new ArrayList<>();
+        Arrays.sort(candidates);
+
+        backtrack(result, new ArrayList<>(), candidates, target, 0);
+
+        return result;
+    }
+
+    private void backtrack(List<List<Integer>> result, List<Integer> current, int[] candidates, int target, int start) {
+        if (target == 0) {
+            result.add(new ArrayList<>(current));
+            return;
+        }
+
+        for (int i = start; i < candidates.length; i++) {
+            if (i > start && candidates[i] == candidates[i - 1]) {
+                continue;
+            }
+
+            int num = candidates[i];
+
+            if (num > target) {
+                break;
+            }
+
+            current.add(num);
+            backtrack(result, current, candidates, target - num, i + 1);
+            current.remove(current.size() - 1);
+        }
+    }
+}