四刷46

Author: diguage

Diff for: docs/0046-permutations.adoc

@@ -1,25 +1,36 @@
 [#0046-permutations]
-= 46. Permutations
+= 46. 全排列
 
-{leetcode}/problems/permutations/[LeetCode - Permutations^]
+https://leetcode.cn/problems/permutations/[LeetCode - 46. 全排列 ^]
 
-Given a collection of *distinct* integers, return all possible permutations.
+给定一个不含重复数字的数组 `nums` ，返回其 _所有可能的全排列_ 。你可以 *按任意顺序* 返回答案。
 
-*Example:*
+*示例 1：*
 
-[subs="verbatim,quotes,macros"]
-----
-*Input:* [1,2,3]
-*Output:*
-[
-  [1,2,3],
-  [1,3,2],
-  [2,1,3],
-  [2,3,1],
-  [3,1,2],
-  [3,2,1]
-]
-----
+....
+输入：nums = [1,2,3]
+输出：[[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
+....
+
+*示例 2：*
+
+....
+输入：nums = [0,1]
+输出：[[0,1],[1,0]]
+....
+
+*示例 3：*
+
+....
+输入：nums = [1]
+输出：[[1]]
+....
+
+*提示：*
+
+* `+1 <= nums.length <= 6+`
+* `+-10 <= nums[i] <= 10+`
+* `nums` 中的所有整数 *互不相同*
 
 == 思路分析
 
@@ -93,14 +104,23 @@ include::{sourcedir}/_0046_Permutations_2.java[tag=answer]
 ----
 --
 
-二刷::
+三刷::
 +
 --
 [{java_src_attr}]
 ----
 include::{sourcedir}/_0046_Permutations_3.java[tag=answer]
 ----
 --
+
+四刷::
++
+--
+[{java_src_attr}]
+----
+include::{sourcedir}/_0046_Permutations_4.java[tag=answer]
+----
+--
 ====
 
 == 参考资料

Diff for: logbook/202503.adoc

@@ -165,11 +165,16 @@ endif::[]
 |{doc_base_url}/0033-search-in-rotated-sorted-array.adoc[题解]
 |⭕️ 重点关注有序部分，优先在有序部分查找，不在有序部分再去无序部分查找。注意判定有序部分的方法： `nums[0]` 与 `nums[mid]` 相比较，而不是 `nums[left]`（它的值会来回变）。
 
-|{counter:codes}
+|{counter:codes2503}
 |{leetcode_base_url}/number-of-islands/[200. 岛屿数量^]
 |{doc_base_url}/0200-number-of-islands.adoc[题解]
 |✅ 想尝试并查集，结果失败。还是沉岛大法好啊！
 
+|{counter:codes2503}
+|{leetcode_base_url}/permutations/[46. 全排列^]
+|{doc_base_url}/0046-permutations.adoc[题解]
+|✅ 回溯
+
 |===
 
 截止目前，本轮练习一共完成 {codes2503} 道题。

Diff for: src/main/java/com/diguage/algo/leetcode/_0046_Permutations_4.java

@@ -0,0 +1,34 @@
+package com.diguage.algo.leetcode;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class _0046_Permutations_4 {
+  // tag::answer[]
+  /**
+   * @author D瓜哥 · https://www.diguage.com
+   * @since 2024-09-18 22:11:50
+   */
+  public List<List<Integer>> permute(int[] nums) {
+    List<List<Integer>> result = new ArrayList<>();
+    backtrack(nums, result, new ArrayList<>(), new boolean[nums.length]);
+    return result;
+  }
+
+  private void backtrack(int[] nums, List<List<Integer>> result, List<Integer> added, boolean[] used) {
+    if (added.size() == nums.length) {
+      result.add(new ArrayList<>(added));
+    }
+    for (int i = 0; i < nums.length; i++) {
+      if (used[i]) {
+        continue;
+      }
+      used[i] = true;
+      added.add(nums[i]);
+      backtrack(nums, result, added, used);
+      used[i] = false;
+      added.remove(added.size() - 1);
+    }
+  }
+  // end::answer[]
+}