[add] LeetCode 46. Permutations

Author: brianway

algorithms-leetcode/README.md

@@ -51,6 +51,7 @@ Leetcode problems classified by company:
 |39|Combination Sum|Medium|Backtracking||
 |41|First Missing Positive|Hard|Hash Table|一题多解|
 |45|Jump Game II|Medium|Dynamic Programming/Greedy|一题多解|
+|46|Permutations|Medium|Backtracking||
 |53|Maximum Subarray|Medium|Dynamic Programming/divide and conquer|一题多解|
 |55|Jump Game|Medium|Greedy||
 |62|Unique Paths|Medium|||

algorithms-leetcode/src/main/java/com/brianway/learning/algorithms/leetcode/medium/LongestSubstringWithoutRepeatingCharacters.java

@@ -7,8 +7,8 @@
  * LeetCode 3. Longest Substring Without Repeating Characters
  * Question: https://leetcode.com/problems/longest-substring-without-repeating-characters/
  * 关键题设:  无
- * * @auther brian
  *
+ * @auther brian
  * @since 2022/11/30 23:37
  */
 public class LongestSubstringWithoutRepeatingCharacters {
@@ -19,7 +19,7 @@ public int lengthOfLongestSubstring(String s) {
 
     /**
      * 滑动窗口+hash表
-     *
+     * <p>
      * 测试用例："tmmzuxt"
      */
     public class LongestSubstringWithoutRepeatingCharacters0 extends LongestSubstringWithoutRepeatingCharacters {

algorithms-leetcode/src/main/java/com/brianway/learning/algorithms/leetcode/medium/Permutations.java

@@ -0,0 +1,56 @@
+package com.brianway.learning.algorithms.leetcode.medium;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.LinkedList;
+import java.util.List;
+
+/**
+ * LeetCode 46. Permutations
+ * Question: https://leetcode.com/problems/permutations/
+ * 关键题设:  无
+ *
+ * @auther brian
+ * @since 2022/12/1 23:08
+ */
+public class Permutations {
+
+    public List<List<Integer>> permute(int[] nums) {
+        return null;
+    }
+
+    public class Permutations0 extends Permutations {
+        @Override
+        public List<List<Integer>> permute(int[] nums) {
+            List<List<Integer>> result = new ArrayList<>();
+            List<Integer> numbers = new ArrayList<Integer>();
+            for (int num : nums) {
+                numbers.add(num);
+            }
+
+            backtracking(result, new LinkedList<>(), numbers, 0);
+            return result;
+        }
+
+        /**
+         * @param result
+         * @param path
+         * @param nums
+         * @param start
+         */
+        public void backtracking(List<List<Integer>> result, LinkedList<Integer> path, List<Integer> nums, int start) {
+            if (start == nums.size()) {
+                result.add(new ArrayList<>(path));
+            }
+
+            for (int i = start; i < nums.size(); i++) {
+                path.push(nums.get(i));
+                Collections.swap(nums, i, start);
+                backtracking(result, path, nums, start + 1);
+                Collections.swap(nums, start, i);
+                path.pop();
+            }
+        }
+
+    }
+}