[FE] Coding Challenge - Tran Quoc Dat

.gitignore

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+# Dependencies
+node_modules/
+**/node_modules/
+
+# Build outputs
+dist/
+**/dist/
+build/
+**/build/
+
+# Test coverage
+coverage/
+**/coverage/
+.nyc_output/
+
+# Logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+lerna-debug.log*
+
+# OS files
+.DS_Store
+.DS_Store?
+._*
+.Spotlight-V100
+.Trashes
+ehthumbs.db
+Thumbs.db
+
+# IDE files
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+.project
+.classpath
+.settings/
+
+# Environment variables
+.env
+.env.local
+.env.*.local
+

src/problem1/.gitignore

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+node_modules/
+dist/
+coverage/
+*.log
+.DS_Store
+

src/problem1/README.md

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+***Performance Comparision***
+| Approach         | Time Complexity | Space Complexity | Notes                  |
+| ---------------- | --------------- | ---------------- | ---------------------- |
+| **Math formula** | O(1)            | O(1)             | Fastest possible       |
+| **For loop**     | O(n)            | O(1)             | Fast, predictable      |
+| **Array.reduce** | O(n)            | O(n)             | N/A                    |
+
+***Pros & Cons***
+**Math Formular**
+*Pros*
+- Fastest
+- Lowest complextiy
+- Shortest
+*Cons*
+- Require knowing the formula
+
+**For loop**
+*Pros*
+- Fast
+- Low complexity
+- Easy to debug
+*Cons*
+- Slightly more verbose than formula
+
+**Array.reduce**
+*Pros*
+- Functional and expressive
+- Declaritive style
+- Easy to chain with other array operations
+*Cons*
+- Worst memory usage among all options

src/problem1/index.test.ts

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+import { sum_to_n_a, sum_to_n_b, sum_to_n_c } from './index';
+
+describe('Approach A', () => {
+  test('sum_to_n_a should return the correct sum', () => {
+    expect(sum_to_n_a(0)).toBe(0);
+    expect(sum_to_n_a(1)).toBe(1);
+    expect(sum_to_n_a(2)).toBe(3);
+    expect(sum_to_n_a(3)).toBe(6);
+    expect(sum_to_n_a(4)).toBe(10);
+  });
+});
+
+describe('Approach B', () => {
+  test('sum_to_n_b should return the correct sum', () => {
+    expect(sum_to_n_b(0)).toBe(0);
+    expect(sum_to_n_b(1)).toBe(1);
+    expect(sum_to_n_b(2)).toBe(3);
+    expect(sum_to_n_b(3)).toBe(6);
+    expect(sum_to_n_b(4)).toBe(10);
+  });
+});
+
+describe('Approach C', () => {
+  test('sum_to_n_c should return the correct sum', () => {
+    expect(sum_to_n_c(0)).toBe(0);
+    expect(sum_to_n_c(1)).toBe(1);
+    expect(sum_to_n_c(2)).toBe(3);
+    expect(sum_to_n_c(3)).toBe(6);
+    expect(sum_to_n_c(4)).toBe(10);
+  });
+});

src/problem1/index.ts

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+type SumToN = (n: number) => number;
+
+export const sum_to_n_a: SumToN = (n) => {
+    if (n <= 1) return n;
+    if (Number.isNaN(n)) throw new Error('Invalid input');
+    return (n * (n + 1)) / 2;
+}
+
+export const sum_to_n_b: SumToN = (n) => {
+    if (n <= 1) return n;
+    if (Number.isNaN(n)) throw new Error('Invalid input');
+    let sum = 0;
+    for (let i = 1; i <= n; i++) {
+        sum += i;
+    }
+    return sum;
+}
+
+export const sum_to_n_c: SumToN = (n) => {
+    if (n <= 1) return n;
+    if (Number.isNaN(n)) throw new Error('Invalid input');
+    return Array.from({ length: n }, (_, i) => i + 1).reduce((acc, curr) => acc + curr, 0);
+}

src/problem1/jest.config.js

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+module.exports = {
+  preset: 'ts-jest',
+  testEnvironment: 'node',
+  roots: ['<rootDir>'],
+  testMatch: ['**/__tests__/**/*.ts', '**/?(*.)+(spec|test).ts'],
+  transform: {
+    '^.+\\.ts$': 'ts-jest',
+  },
+  collectCoverageFrom: [
+    '*.ts',
+    '!*.test.ts',
+    '!*.spec.ts',
+    '!**/__tests__/**',
+  ],
+  moduleFileExtensions: ['ts', 'js', 'json'],
+  verbose: true,
+};
+