From e39c2e5e6caac828c36bb6d6ba533476b188be25 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=EA=B9=80=EC=84=A0=EB=AF=BC?= <tjsals116@gmail.com>
Date: Mon, 26 Aug 2024 23:59:04 +0900
Subject: [PATCH 1/3] Add week 3 solutions: two-sum

---
 two-sum/gitsunmin.ts | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
 create mode 100644 two-sum/gitsunmin.ts

diff --git a/two-sum/gitsunmin.ts b/two-sum/gitsunmin.ts
new file mode 100644
index 000000000..23863c12d
--- /dev/null
+++ b/two-sum/gitsunmin.ts
@@ -0,0 +1,16 @@
+/**
+ * https://leetcode.com/problems/two-sum
+ * time complexity : O(n)
+ * space complexity : O(n)
+ */
+function twoSum(nums: number[], target: number): number[] {
+    const m = new Map<number, number>();
+
+    for (let i = 0; i < nums.length; i++) {
+        if (m.has(nums[i]))
+            return [m.get(nums[i]), i];
+        m.set(target - nums[i], i);
+    }
+
+    return [-1, -1];
+};

From 65ce8e5cb807cd34d60258d13efeedc032a9be75 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=EA=B9=80=EC=84=A0=EB=AF=BC?= <tjsals116@gmail.com>
Date: Tue, 27 Aug 2024 19:54:38 +0900
Subject: [PATCH 2/3] Add week 3 solutions: climbing-stairs

---
 climbing-stairs/gitsunmin.ts | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)
 create mode 100644 climbing-stairs/gitsunmin.ts

diff --git a/climbing-stairs/gitsunmin.ts b/climbing-stairs/gitsunmin.ts
new file mode 100644
index 000000000..e87319fa4
--- /dev/null
+++ b/climbing-stairs/gitsunmin.ts
@@ -0,0 +1,17 @@
+/**
+ * https://leetcode.com/problems/climbing-stairs
+ * time complexity : O(n)
+ * space complexity : O(1)
+ */
+
+export const upStairs = (n: number): number => {
+    let [l, r] = [1, 2];
+    for (let i = 3; i <= n; i++) [l, r] = [r, l + r];
+
+    return r;
+};
+
+export function climbStairs(n: number): number {
+    if (n <= 2) return n;
+    return upStairs(n);
+};

From 788607c6f9b017f7cb4d61a8f5a04f9abe8bf0d8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=EA=B9=80=EC=84=A0=EB=AF=BC?= <tjsals116@gmail.com>
Date: Fri, 30 Aug 2024 23:51:30 +0900
Subject: [PATCH 3/3] Add week 3 solutions: product-of-array-except-self

---
 product-of-array-except-self/gitsunmin.ts | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 product-of-array-except-self/gitsunmin.ts

diff --git a/product-of-array-except-self/gitsunmin.ts b/product-of-array-except-self/gitsunmin.ts
new file mode 100644
index 000000000..3d06fa5c3
--- /dev/null
+++ b/product-of-array-except-self/gitsunmin.ts
@@ -0,0 +1,23 @@
+/**
+ * https://leetcode.com/problems/product-of-array-except-self
+ * time complexity : O(n)
+ * space complexity : O(1)
+ */
+function productExceptSelf(nums: number[]): number[] {
+    const n = nums.length;
+    const answer = new Array(n).fill(1);
+
+    let leftProduct = 1;
+    for (let i = 0; i < n; i++) {
+        answer[i] = leftProduct;
+        leftProduct *= nums[i];
+    }
+
+    let rightProduct = 1;
+    for (let i = n - 1; i >= 0; i--) {
+        answer[i] *= rightProduct;
+        rightProduct *= nums[i];
+    }
+
+    return answer;
+}