[BE]: Code Challenge - Le Quoc Huy (Viet Nam)

.gitignore

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+.env
+node_modules/
+dist/
+*.sqlite
+*.sqlite-shm
+*.sqlite-wal
+.DS_Store

src/problem4/README.md

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+# Sum To N Challenge
+
+Three TypeScript implementations of `sum_to_n`.
+
+## Behavior
+
+- `n > 0`: sum from `1` to `n`
+- `n = 0`: return `0`
+- `n < 0`: sum from `n` to `-1`
+- Non-integer or unsafe values throw an error
+
+## Approaches
+
+- `sum_to_n_a`: iterative loop
+- `sum_to_n_b`: arithmetic formula
+- `sum_to_n_c`: pair-from-ends loop
+
+## Run
+
+```bash
+npm run build
+npm test
+```
+
+## Files
+
+- `src/sum-to-n.ts`: implementations
+- `test/sum-to-n.test.ts`: test cases

src/problem4/package.json

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+{
+    "name": "sum-to-n-challenge",
+    "version": "1.0.0",
+    "private": true,
+    "description": "Three TypeScript implementations for summation to n.",
+    "scripts": {
+        "build": "tsc -p tsconfig.json --pretty false",
+        "test": "npm run build && node dist/test/sum-to-n.test.js"
+    }
+}

src/problem4/src/sum-to-n.ts

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+function assertSafeInteger(n: number): void {
+    if (!Number.isSafeInteger(n)) {
+        throw new TypeError("n must be a safe integer");
+    }
+}
+
+// Approach A: Iterative loop.
+export function sum_to_n_a(n: number): number {
+    assertSafeInteger(n);
+
+    let sum = 0;
+
+    if (n >= 0) {
+        for (let i = 1; i <= n; i += 1) {
+            sum += i;
+        }
+
+        return sum;
+    }
+
+    for (let i = n; i <= -1; i += 1) {
+        sum += i;
+    }
+
+    return sum;
+}
+
+// Approach B: Math formula.
+export function sum_to_n_b(n: number): number {
+    assertSafeInteger(n);
+
+    const abs = Math.abs(n);
+    const sum = (abs * (abs + 1)) / 2;
+
+    return n < 0 ? -sum : sum;
+}
+
+// Approach C: Pair values from both ends of the range.
+export function sum_to_n_c(n: number): number {
+    assertSafeInteger(n);
+
+    if (n === 0) {
+        return 0;
+    }
+
+    let left = n > 0 ? 1 : n;
+    let right = n > 0 ? n : -1;
+    let sum = 0;
+
+    while (left < right) {
+        sum += left + right;
+        left += 1;
+        right -= 1;
+    }
+
+    if (left === right) {
+        sum += left;
+    }
+
+    return sum;
+}

src/problem4/test/sum-to-n.test.ts

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+import { sum_to_n_a, sum_to_n_b, sum_to_n_c } from "../src/sum-to-n";
+
+type SumFunction = (n: number) => number;
+
+const implementations: Array<[string, SumFunction]> = [
+    ["sum_to_n_a", sum_to_n_a],
+    ["sum_to_n_b", sum_to_n_b],
+    ["sum_to_n_c", sum_to_n_c],
+];
+
+const validCases: Array<[number, number]> = [
+    [0, 0],
+    [1, 1],
+    [2, 3],
+    [5, 15],
+    [10, 55],
+    [100, 5050],
+    [-1, -1],
+    [-2, -3],
+    [-5, -15],
+    [-10, -55],
+    [100000, 5000050000],
+    [-100000, -5000050000],
+];
+
+const invalidCases = [
+    Number.NaN,
+    Number.POSITIVE_INFINITY,
+    Number.NEGATIVE_INFINITY,
+    1.5,
+    Number.MAX_SAFE_INTEGER + 1,
+];
+
+function assertEqual(actual: number, expected: number, label: string): void {
+    if (actual !== expected) {
+        throw new Error(`${label}: expected ${expected}, received ${actual}`);
+    }
+}
+
+function assertThrows(run: () => unknown, label: string): void {
+    let threw = false;
+
+    try {
+        run();
+    } catch {
+        threw = true;
+    }
+
+    if (!threw) {
+        throw new Error(`${label}: expected an error`);
+    }
+}
+
+function logPass(message: string): void {
+    console.log(`[PASS] ${message}`);
+}
+
+let passed = 0;
+
+for (const [name, fn] of implementations) {
+    console.log(`\nRUNNING ${name}...`);
+
+    for (const [input, expected] of validCases) {
+        assertEqual(fn(input), expected, `${name}(${input})`);
+        logPass(`${name}(${input}) => ${expected}`);
+        passed += 1;
+    }
+
+    for (const input of invalidCases) {
+        assertThrows(() => fn(input), `${name}(${String(input)})`);
+        logPass(`${name}(${String(input)}) throws ERROR`);
+        passed += 1;
+    }
+}
+
+console.log(`All tests passed (${passed} checks).`);

src/problem4/tsconfig.json

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+{
+    "compilerOptions": {
+        "target": "ES2022",
+        "module": "node16",
+        "moduleResolution": "node16",
+        "strict": true,
+        "esModuleInterop": true,
+        "forceConsistentCasingInFileNames": true,
+        "skipLibCheck": true,
+        "rootDir": ".",
+        "outDir": "dist"
+    },
+    "include": ["src/**/*.ts", "test/**/*.ts"]
+}

src/problem5/.gitignore

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+.env
+node_modules/
+dist/
+*.sqlite
+*.sqlite-shm
+*.sqlite-wal
+.DS_Store