#feat:leetcode p39题题解

src/leetcode/p39/Solution.java

@@ -0,0 +1,63 @@
+package leetcode.p39;
+
+import java.util.*;
+
+/**
+ * @ProjectName: LeetCode
+ * @FileName: Solution
+ * @Author: 杨逸
+ * @Data:2026/3/8 19:13
+ * @Description: https://leetcode.cn/problems/combination-sum/description/
+ * 39. 组合总和
+ */
+public class Solution {
+    /**
+     * 回溯法
+     * @param candidates
+     * @param target
+     * @return {@code List<List<Integer>> }
+     * @description:
+     * @author: 杨逸
+     * @data:2026/03/08 19:28:31
+     * @since 1.0.0
+     */
+    public List<List<Integer>> combinationSum(int[] candidates, int target) {
+        List<List<Integer>> result = new ArrayList<>();
+        //储存格式:元素个数-元素乘积
+        HashSet<String> set = new HashSet<>();
+        dfs(0,0,new LinkedList<>(),candidates,target,result);
+        return result;
+    }
+
+    /**
+     * @param index 当前遍历的元素下标
+     * @param current 当前元素的和
+     * @param deque 当前元素列表
+     * @param candidates 候选元素列表
+     * @param target 目标值
+     * @param result 结果列表
+     * @description:
+     * @author: 杨逸
+     * @data:2026/03/08 20:03:34
+     * @since 1.0.0
+     */
+    private void dfs(int index,int current, Deque<Integer> deque,int[] candidates,int target,List<List<Integer>> result) {
+        if (current == target) {
+            //记录符合要求的记录
+            List<Integer> list = List.copyOf(deque);
+            result.add(list);
+            return;
+        }
+        if (current > target || index >= candidates.length) {
+            //递归结束
+            return;
+        }
+        //选,选当前这个(下次还可以选)
+        deque.addLast(candidates[index]);
+        dfs(index,current+candidates[index],deque,candidates,target,result);
+        //还原现场
+        deque.removeLast();
+        //不选,选下一个
+        dfs(index+1,current,deque,candidates,target,result);
+    }
+}