[BE] Code Challenge - Lam Dao Cuong

src/problem4/solution.ts

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+// Problem 4: Three ways to sum to n (TypeScript)
+// ================================================
+
+/**
+ * Method 1: Iterative approach using a for loop
+ * 
+ * Time Complexity: O(n) - loops n times
+ * Space Complexity: O(1) - only uses a single variable for sum
+ * 
+ * Efficiency: Simple and straightforward, but slower for large n
+ * Use case: Good for small to medium values of n, easy to understand
+ */
+function sum_to_n_a(n: number): number {
+  let sum = 0;
+  for (let i = 1; i <= n; i++) {
+    sum += i;
+  }
+  return sum;
+}
+
+/**
+ * Method 2: Mathematical formula (Gauss formula)
+ * Formula: n * (n + 1) / 2
+ * 
+ * Time Complexity: O(1) - constant time, single calculation
+ * Space Complexity: O(1) - no additional space needed
+ * 
+ * Efficiency: Most efficient approach, instant calculation regardless of n
+ * Use case: Best for any size of n, especially large values
+ * Note: This is the optimal solution
+ */
+function sum_to_n_b(n: number): number {
+  return (n * (n + 1)) / 2;
+}
+
+/**
+ * Method 3: Recursive approach
+ * 
+ * Time Complexity: O(n) - makes n recursive calls
+ * Space Complexity: O(n) - call stack grows to n depth
+ * 
+ * Efficiency: Least efficient due to function call overhead and stack usage
+ * Use case: Demonstrates recursion concept but not recommended for large n
+ * Warning: May cause stack overflow for very large values of n
+ */
+function sum_to_n_c(n: number): number {
+  if (n <= 1) {
+    return n;
+  }
+  return n + sum_to_n_c(n - 1);
+}
+
+// Test cases
+console.log('Testing sum_to_n_a:');
+console.log(`sum_to_n_a(5) = ${sum_to_n_a(5)}`); // Expected: 15
+console.log(`sum_to_n_a(10) = ${sum_to_n_a(10)}`); // Expected: 55
+console.log(`sum_to_n_a(100) = ${sum_to_n_a(100)}`); // Expected: 5050
+
+console.log('\nTesting sum_to_n_b:');
+console.log(`sum_to_n_b(5) = ${sum_to_n_b(5)}`); // Expected: 15
+console.log(`sum_to_n_b(10) = ${sum_to_n_b(10)}`); // Expected: 55
+console.log(`sum_to_n_b(100) = ${sum_to_n_b(100)}`); // Expected: 5050
+
+console.log('\nTesting sum_to_n_c:');
+console.log(`sum_to_n_c(5) = ${sum_to_n_c(5)}`); // Expected: 15
+console.log(`sum_to_n_c(10) = ${sum_to_n_c(10)}`); // Expected: 55
+console.log(`sum_to_n_c(100) = ${sum_to_n_c(100)}`); // Expected: 5050

src/problem4/tsconfig.json

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+{
+  "compilerOptions": {
+    "target": "ES2020",
+    "module": "commonjs",
+    "lib": ["ES2020"],
+    "moduleResolution": "node",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "resolveJsonModule": true,
+    "outDir": "./dist",
+    "types": ["node"]
+  },
+  "include": ["*.ts"],
+  "exclude": ["node_modules", "dist"]
+}

src/problem5/.env.example

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+PORT=3000
+NODE_ENV=development

src/problem5/.gitignore

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+node_modules
+dist
+.env
+*.log
+.DS_Store
+data/*.json
+!data/.gitkeep