三刷40

Author: diguage

docs/0040-combination-sum-ii.adoc

@@ -71,6 +71,15 @@ include::{sourcedir}/_0040_CombinationSumII.java[tag=answer]
 include::{sourcedir}/_0040_CombinationSumII_2.java[tag=answer]
 ----
 --
+
+三刷::
++
+--
+[{java_src_attr}]
+----
+include::{sourcedir}/_0040_CombinationSumII_3.java[tag=answer]
+----
+--
 ====
 
 == 参考资料

logbook/202406.adoc

@@ -635,6 +635,11 @@
 |{doc_base_url}/0102-binary-tree-level-order-traversal.adoc[题解]
 |✅广度优先遍历
 
+|{counter:codes}
+|{leetcode_base_url}/combination-sum-ii/[40. Combination Sum II^]
+|{doc_base_url}/0040-combination-sum-ii.adoc[题解]
+|✔️组合，回溯，剪枝
+
 |===
 
 截止目前，本轮练习一共完成 {codes} 道题。

src/main/java/com/diguage/algo/leetcode/_0040_CombinationSumII_2.java

@@ -20,29 +20,29 @@ public List<List<Integer>> combinationSum2(int[] candidates, int target) {
     return result;
   }
 
-  private void backtrack(int[] can, List<List<Integer>> result,
-                         int start, int target, List<Integer> com) {
+  private void backtrack(int[] candidates, List<List<Integer>> result,
+                         int start, int target, List<Integer> path) {
     // 子集和等于 target 时，记录解
     if (target == 0) {
-      result.add(new ArrayList<>(com));
+      result.add(new ArrayList<>(path));
       return;
     }
     // 剪枝二：从 start 开始遍历，避免生成重复子集
     // 剪枝三：从 start 开始遍历，避免重复选择同一元素
-    for (int i = start; i < can.length; i++) {
+    for (int i = start; i < candidates.length; i++) {
       // 剪枝一：若子集和超过 target ，则直接结束循环
       // 这是因为数组已排序，后边元素更大，子集和一定超过 target
-      if (target < can[i]) {
+      if (target < candidates[i]) {
         break;
       }
       // 剪枝四：如果该元素与左边元素相等，说明该搜索分支重复，直接跳过
-      if (start < i && can[i - 1] == can[i]) {
+      if (start < i && candidates[i - 1] == candidates[i]) {
         continue;
       }
-      com.add(can[i]);
+      path.add(candidates[i]);
       // 进行下一轮选择
-      backtrack(can, result, i + 1, target - can[i], com);
-      com.remove(com.size() - 1);
+      backtrack(candidates, result, i + 1, target - candidates[i], path);
+      path.remove(path.size() - 1);
     }
   }
   // end::answer[]

src/main/java/com/diguage/algo/leetcode/_0040_CombinationSumII_3.java

@@ -0,0 +1,41 @@
+package com.diguage.algo.leetcode;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class _0040_CombinationSumII_3 {
+  // tag::answer[]
+
+  /**
+   * @author D瓜哥 · https://www.diguage.com
+   * @since 2024-09-16 17:31:07
+   */
+  public List<List<Integer>> combinationSum2(int[] candidates, int target) {
+    Arrays.sort(candidates);
+    List<List<Integer>> result = new ArrayList<>();
+    backtrack(candidates, target, result, 0, new ArrayList<>());
+    return result;
+  }
+
+  private void backtrack(int[] candidates, int target,
+                         List<List<Integer>> result, int start, List<Integer> path) {
+    if (target == 0) {
+      result.add(new ArrayList(path));
+      return;
+    }
+    for (int i = start; i < candidates.length; i++) {
+      int num = candidates[i];
+      if (target < num) {
+        break;
+      }
+      if (start < i && candidates[i - 1] == candidates[i]) {
+        continue;
+      }
+      path.add(num);
+      backtrack(candidates, target - num, result, i + 1, path);
+      path.remove(path.size() - 1);
+    }
+  }
+  // end::answer[]
+}