99techteam · vietanh1606 · Apr 29, 2026 · Apr 29, 2026 · Apr 29, 2026
diff --git a/src/problem1/README.md b/src/problem1/README.md
@@ -0,0 +1,51 @@
+# Problem 1: Three Ways to Sum to N
+
+This solution provides three unique JavaScript implementations of `sum_to_n`.
+
+## Files
+
+- `solution.js`: contains all three implementations.
+
+## Implementations
+
+1. `sum_to_n_a`
+
+   Iterative loop approach. It loops from `1` to `|n|`, adds each number to an accumulator, and applies the original sign of `n`.
+
+   Complexity: `O(n)` time, `O(1)` space.
+
+2. `sum_to_n_b`
+
+   Mathematical approach using the Gauss formula:
+
+   ```js
+   n * (n + 1) / 2
+   ```
+
+   The implementation uses `Math.abs(n)` and reapplies the sign, so negative integers are handled consistently.
+
+   Complexity: `O(1)` time, `O(1)` space.
+
+3. `sum_to_n_c`
+
+   Array reduce approach. It builds a range from `1` to `|n|`, applies the sign, then sums the values with `reduce`.
+
+   Complexity: `O(n)` time, `O(n)` space.
+
+## Notes
+
+The task states that `n` can be any integer. This implementation supports:
+
+- positive integers, for example `sum_to_n(5) === 15`
+- zero, where `sum_to_n(0) === 0`
+- negative integers, for example `sum_to_n(-3) === -6`
+
+## Quick test
+
+Open `solution.js` in a browser console or include it with a script tag. Then call:
+
+```js
+sum_to_n_a(5); // 15
+sum_to_n_b(5); // 15
+sum_to_n_c(5); // 15
+```
diff --git a/src/problem1/solution.js b/src/problem1/solution.js
@@ -0,0 +1,45 @@
+var sum_to_n_a = function(n) {
+    // Idea: Iterative approach. Use a loop to add each number from 1 to |n|.
+    // Complexity: Time O(n), Space O(1).
+    if (n === 0) {
+        return 0;
+    }
+
+    var sign = n > 0 ? 1 : -1;
+    var total = 0;
+
+    for (var i = 1; i <= Math.abs(n); i++) {
+        total += i * sign;
+    }
+
+    return total;
+};
+
+var sum_to_n_b = function(n) {
+    // Idea: Mathematical approach. Use the Gauss formula n * (n + 1) / 2.
+    // Complexity: Time O(1), Space O(1).
+    if (n === 0) {
+        return 0;
+    }
+
+    var absN = Math.abs(n);
+    var result = absN * (absN + 1) / 2;
+
+    return n > 0 ? result : -result;
+};
+
+var sum_to_n_c = function(n) {
+    // Idea: Array reduce approach. Build a range from 1 to |n| and reduce it to a sum.
+    // Complexity: Time O(n), Space O(n).
+    if (n === 0) {
+        return 0;
+    }
+
+    var sign = n > 0 ? 1 : -1;
+
+    return Array.from({ length: Math.abs(n) }, function(_, index) {
+        return (index + 1) * sign;
+    }).reduce(function(total, current) {
+        return total + current;
+    }, 0);
+};
diff --git a/src/problem2/README.md b/src/problem2/README.md
@@ -0,0 +1,35 @@
+# Problem 2: Fancy Form
+
+A Vite + React currency swap form using live token prices from Switcheo.
+
+## Preview
+
+![Currency swap form preview](./docs/screenshot.png)
+
+## Run locally
+
+```bash
+npm install
+npm run dev
+```
+
+Open the local URL printed by Vite, usually:
+
+```text
+http://localhost:5173/
+```
+
+## Build
+
+```bash
+npm run build
+```
+
+## Features
+
+- Live token price loading with fallback demo prices.
+- Token selector with token icons and USD prices.
+- Automatic receive amount and exchange-rate calculation.
+- Input validation for amount, same-token swaps, and insufficient balance.
+- Mock swap confirmation with loading state.
+- Responsive UI built with Tailwind CSS.
diff --git a/src/problem2/docs/screenshot.png b/src/problem2/docs/screenshot.png
diff --git a/src/problem2/index.html b/src/problem2/index.html
@@ -1,27 +1,15 @@
-<html>
+<!DOCTYPE html>
+<html lang="en">
 
 <head>
+  <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <title>Fancy Form</title>
-
-  <!-- You may add more stuff here -->
-  <link href="style.css" rel="stylesheet" />
 </head>
 
 <body>
-
-  <!-- You may reorganise the whole HTML, as long as your form achieves the same effect. -->
-  <form onsubmit="return !1">
-    <h5>Swap</h5>
-    <label for="input-amount">Amount to send</label>
-    <input id="input-amount" />
-
-    <label for="output-amount">Amount to receive</label>
-    <input id="output-amount" />
-
-    <button>CONFIRM SWAP</button>
-  </form>
-  <script src="script.js"></script>
+  <div id="root"></div>
+  <script type="module" src="/src/main.jsx"></script>
 </body>
 
 </html>