238th Commit

Author: Shyam-Chen

README.md

@@ -468,15 +468,17 @@ Must-do List for Interview Prep
 
 [208]: ./src/page-2/208.%20Implement%20Trie%20(Prefix%20Tree)/Trie.ts
 
-| Backtracking                              |          |        |
-| ----------------------------------------- | -------- | ------ |
-| 17. Letter Combinations of a Phone Number | Solution | Medium |
-| 77. Combinations                          | Solution | Medium |
-| 46. Permutations                          | Solution | Medium |
-| 39. Combination Sum                       | Solution | Medium |
-| 52. N-Queens II                           | Solution | Hard   |
-| 22. Generate Parentheses                  | Solution | Medium |
-| 79. Word Search                           | Solution | Medium |
+| Backtracking                              |                |        |
+| ----------------------------------------- | -------------- | ------ |
+| 17. Letter Combinations of a Phone Number | Solution       | Medium |
+| 77. Combinations                          | Solution       | Medium |
+| 46. Permutations                          | [Solution][46] | Medium |
+| 39. Combination Sum                       | Solution       | Medium |
+| 52. N-Queens II                           | Solution       | Hard   |
+| 22. Generate Parentheses                  | Solution       | Medium |
+| 79. Word Search                           | Solution       | Medium |
+
+[46]: ./src/page-1/46.%20Permutations/permute.ts
 
 | Divide & Conquer                                |                 |        |
 | ----------------------------------------------- | --------------- | ------ |
@@ -584,13 +586,14 @@ Must-do List for Interview Prep
 | 17. Letter Combinations of a Phone Number | [Solution][17] | Medium |
 | 22. Generate Parentheses                  | Solution       | Medium |
 | 39. Combination Sum                       | Solution       | Medium |
-| 46. Permutations                          | Solution       | Medium |
+| 46. Permutations                          | [Solution][46] | Medium |
 | 51. N-Queens                              | Solution       | Hard   |
 | 78. Subsets                               | Solution       | Medium |
 | 79. Word Search                           | Solution       | Medium |
 | 131. Palindrome Partitioning              | Solution       | Medium |
 
 [17]: ./src/page-1/17.%20Letter%20Combinations%20of%20a%20Phone%20Number/letterCombinations.ts
+[46]: ./src/page-1/46.%20Permutations/permute.ts
 
 | Binary Search                                               |                |        |
 | ----------------------------------------------------------- | -------------- | ------ |

algorithms/13.backtracking/README.md

@@ -31,65 +31,10 @@ flowchart TB
     2 -. 剪枝 .-> 6
 ```
 
-```ts
-[1, 2, 3];
-```
-
-```ts
-[
-  [1, 2, 3],
-  [1, 3, 2],
-  [2, 1, 3],
-  [2, 3, 1],
-  [3, 1, 2],
-  [3, 2, 1],
-];
-```
-
-```mermaid
-flowchart TB
-    0(_, _, _)
-    1(1, _, _)
-    2(2, _, _)
-    3(3, _, _)
-
-    4(1, 2, _)
-    5(1, 3, _)
-    6(2, 1, _)
-    7(2, 3, _)
-    8(3, 1, _)
-    9(3, 2, _)
-
-    10(1, 2, 3)
-    11(1, 3, 2)
-    12(2, 1, 3)
-    13(2, 3, 1)
-    14(3, 1, 2)
-    15(3, 2, 1)
-
-    0 --> 1
-    0 --> 2
-    0 --> 3
-
-    1 --> 4
-    1 --> 5
-    2 --> 6
-    2 --> 7
-    3 --> 8
-    3 --> 9
-
-    4 --> 10
-    5 --> 11
-    6 --> 12
-    7 --> 13
-    8 --> 14
-    9 --> 15
-```
-
 ```ts
 function permute(nums: number[]): number[][] {
   const result: number[][] = [];
-  const used: boolean[] = Array(nums.length).fill(false);
+  const selected: boolean[] = Array(nums.length).fill(false);
 
   function backtrack(currentPermutation: number[]) {
     // 如果當前排列的長度等於原數組長度，說明我們已經生成了一個完整排列
@@ -101,18 +46,18 @@ function permute(nums: number[]): number[][] {
     // 走訪可用數字
     for (let i = 0; i < nums.length; i++) {
       // 如果該數字已經被選過，則跳過 (剪枝)
-      if (used[i]) continue;
+      if (selected[i]) continue;
 
       // 做選擇
       currentPermutation.push(nums[i]);
-      used[i] = true;
+      selected[i] = true;
 
       // 遞迴進行下一步選擇
       backtrack(currentPermutation);
 
       // 撤銷選擇 (回溯)
       currentPermutation.pop();
-      used[i] = false;
+      selected[i] = false;
     }
   }
 

src/page-1/46. Permutations/permute.test.ts

@@ -0,0 +1,21 @@
+import { permute } from './permute';
+
+describe('46. Permutations', () => {
+  test('permute', () => {
+    expect(permute([1, 2, 3])).toStrictEqual([
+      [1, 2, 3],
+      [1, 3, 2],
+      [2, 1, 3],
+      [2, 3, 1],
+      [3, 1, 2],
+      [3, 2, 1],
+    ]);
+
+    expect(permute([0, 1])).toStrictEqual([
+      [0, 1],
+      [1, 0],
+    ]);
+
+    expect(permute([1])).toStrictEqual([[1]]);
+  });
+});

src/page-1/46. Permutations/permute.ts

@@ -0,0 +1,38 @@
+type Permute = (nums: number[]) => number[][];
+
+/**
+ * Accepted
+ */
+export const permute: Permute = (nums) => {
+  const result: number[][] = [];
+  const selected: boolean[] = Array(nums.length).fill(false);
+
+  function backtrack(currentPermutation: number[]) {
+    // If the current permutation's length equals the input array's length, we have a complete permutation
+    if (currentPermutation.length === nums.length) {
+      result.push([...currentPermutation]);
+      return;
+    }
+
+    // Traverse the available numbers
+    for (let i = 0; i < nums.length; i++) {
+      // Skip if the number has already been selected (pruning)
+      if (selected[i]) continue;
+
+      // Make a choice
+      currentPermutation.push(nums[i]);
+      selected[i] = true;
+
+      // Recursively make the next choice
+      backtrack(currentPermutation);
+
+      // Undo the choice (backtrack)
+      currentPermutation.pop();
+      selected[i] = false;
+    }
+  }
+
+  backtrack([]); // Start backtracking
+
+  return result;
+};