[BE] Name - Phyo Zaw Linn | mail: phyozawlinn@ucsy.edu.mm

.gitignore

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+# Problem 4 (Node.js/TypeScript)
+node_modules/
+dist/
+.env
+.env.*
+!.env.example
+
+# Logs
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+
+# Optional TypeScript incremental cache
+*.tsbuildinfo
+
+migrations/

README.md

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+All answers and implementations for Problems 4, 5, and 6 related to the Backend Engineer (Remote) role are documented here.

problem_4/sum_to_n.js

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+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.sum_to_n_a = sum_to_n_a;
+exports.sum_to_n_b = sum_to_n_b;
+exports.sum_to_n_c = sum_to_n_c;
+function sum_to_n_a(n) {
+    //time: O(n), space: O(1)
+    if (n <= 0)
+        return 0;
+    var sum = 0;
+    for (var i = 1; i <= n; i++) {
+        sum += i;
+    }
+    return sum;
+}
+function sum_to_n_b(n) {
+    //time: O(n), space: O(n)
+    if (n <= 0)
+        return 0;
+    if (n === 1)
+        return 1;
+    return n + sum_to_n_b(n - 1);
+}
+function sum_to_n_c(n) {
+    //time: O(1), space: O(1)
+    if (n <= 0)
+        return 0;
+    return (n * (n + 1)) / 2;
+}

problem_4/sum_to_n.ts

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+export function sum_to_n_a(n: number): number {
+    //time: O(n), space: O(1)
+    if (n <= 0) return 0;
+    let sum = 0;
+    for (let i = 1; i <= n; i++) {
+        sum += i;
+    }
+    return sum;
+}
+
+export function sum_to_n_b(n: number): number {
+    //time: O(n), space: O(n)
+    if (n <= 0) return 0;
+    if (n === 1) return 1;
+    return n + sum_to_n_b(n - 1);
+}
+
+export function sum_to_n_c(n: number): number {
+    //time: O(1), space: O(1)
+    if (n <= 0) return 0;
+    return (n * (n + 1)) / 2;
+}
+

problem_4/task.md

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+# Task
+
+Provide 3 unique implementations of the following function in TypeScript.
+
+- Comment on the complexity or efficiency of each function.
+
+**Input**: `n` - any integer
+
+*Assuming this input will always produce a result lesser than `Number.MAX_SAFE_INTEGER`*.
+
+**Output**: `return` - summation to `n`, i.e. `sum_to_n(5) === 1 + 2 + 3 + 4 + 5 === 15`.
+
+```go
+func sum_to_n_a(n: number): number {
+	// your code here
+}
+
+func sum_to_n_b(n: number): number {
+	// your code here
+}
+
+func sum_to_n_c(n: number): number {
+	// your code here
+}
+```

problem_4/test.js

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+const { sum_to_n_a, sum_to_n_b, sum_to_n_c } = require('./sum_to_n');
+
+function expected(n) {
+  if (n <= 0) return 0;
+  return (n * (n + 1)) / 2;
+}
+
+const cases = [-3, 0, 1, 2, 5, 10, 100];
+let allPass = true;
+for (const n of cases) {
+  const a = sum_to_n_a(n);
+  const b = sum_to_n_b(n);
+  const c = sum_to_n_c(n);
+  const exp = expected(n);
+  const pass = (a === exp) && (b === exp) && (c === exp);
+  console.log(`n=${n}: a=${a}, b=${b}, c=${c}, expected=${exp} -> ${pass ? 'PASS' : 'FAIL'}`);
+  if (!pass) allPass = false;
+}
+
+if (!allPass) {
+  console.error('Some tests failed');
+  process.exit(1);
+} else {
+  console.log('All tests passed');
+}

problem_5/.env.example

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+PORT=3000
+DATABASE_URL="postgresql://postgres:postgres@localhost:5432/resources_db?schema=public"