From cf40e6ad0345ccf8463e4e8d292ba43260663648 Mon Sep 17 00:00:00 2001
From: Nancy Lee <saeryounglee@gmail.com>
Date: Thu, 24 Jul 2025 22:18:21 +0900
Subject: [PATCH 1/5] contains duplicate solution

---
 contains-duplicate/nancyel.ts | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
 create mode 100644 contains-duplicate/nancyel.ts

diff --git a/contains-duplicate/nancyel.ts b/contains-duplicate/nancyel.ts
new file mode 100644
index 000000000..f6f199816
--- /dev/null
+++ b/contains-duplicate/nancyel.ts
@@ -0,0 +1,14 @@
+/**
+ * time complexity: O(n)
+ * space complexity: O(n)
+ */
+function containsDuplicate(nums: number[]): boolean {
+  const seen = new Set();
+  for (let num of nums) {
+    if (seen.has(num)) {
+      return true;
+    }
+    seen.add(num);
+  }
+  return false;
+}

From cb574a6ba991e344492e297e002939305fbe940c Mon Sep 17 00:00:00 2001
From: Nancy Lee <saeryounglee@gmail.com>
Date: Thu, 24 Jul 2025 22:44:07 +0900
Subject: [PATCH 2/5] two sum solution

---
 two-sum/nancyel.ts | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
 create mode 100644 two-sum/nancyel.ts

diff --git a/two-sum/nancyel.ts b/two-sum/nancyel.ts
new file mode 100644
index 000000000..8ac5cbb2e
--- /dev/null
+++ b/two-sum/nancyel.ts
@@ -0,0 +1,19 @@
+/**
+ * Time Complexity: O(n) (using a single pass with a hash map)
+ * (If a nested loop was used, it would be O(n^2))
+ */
+function twoSum(nums: number[], target: number): number[] {
+  const numAndIndex = new Map<number, number>();
+
+  for (let i = 0; i < nums.length; i++) {
+    const diff = target - nums[i];
+
+    if (numAndIndex.has(diff)) {
+      return [numAndIndex.get(diff)!, i];
+    }
+
+    numAndIndex.set(nums[i], i);
+  }
+
+  return [];
+}

From f9ab86240f9240602913f92762cd679d8cc5f6e8 Mon Sep 17 00:00:00 2001
From: Nancy Lee <saeryounglee@gmail.com>
Date: Fri, 25 Jul 2025 20:56:24 +0900
Subject: [PATCH 3/5] top k freq solution

---
 top-k-frequent-elements/nancyel.ts | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)
 create mode 100644 top-k-frequent-elements/nancyel.ts

diff --git a/top-k-frequent-elements/nancyel.ts b/top-k-frequent-elements/nancyel.ts
new file mode 100644
index 000000000..5fd093fbd
--- /dev/null
+++ b/top-k-frequent-elements/nancyel.ts
@@ -0,0 +1,21 @@
+/**
+ * time complexity: O(n + m log m),
+ *   n = length of input array
+ *   m = number of unique elements (m ≤ n)
+ * space complexity: O(m)
+ */
+
+function topKFrequent(nums: number[], k: number): number[] {
+  const freqMap = new Map<number, number>();
+
+  // Count frequencies using a map: O(n)
+  for (const num of nums) {
+    freqMap.set(num, (freqMap.get(num) || 0) + 1);
+  }
+
+  // Extract the top k elements
+  return Array.from(freqMap.entries()) // O(m)
+    .sort(([, a], [, b]) => b - a) // O(m log m)
+    .slice(0, k)
+    .map(([num]) => num); // extract the keys only
+}

From 94f2c102a0035c5ca9ac78a6731ef7e264fe13b0 Mon Sep 17 00:00:00 2001
From: Nancy Lee <saeryounglee@gmail.com>
Date: Fri, 25 Jul 2025 21:32:31 +0900
Subject: [PATCH 4/5] longest consecutive seq solution

---
 longest-consecutive-sequence/nancyel.ts | 27 +++++++++++++++++++++++++
 1 file changed, 27 insertions(+)
 create mode 100644 longest-consecutive-sequence/nancyel.ts

diff --git a/longest-consecutive-sequence/nancyel.ts b/longest-consecutive-sequence/nancyel.ts
new file mode 100644
index 000000000..79dc79161
--- /dev/null
+++ b/longest-consecutive-sequence/nancyel.ts
@@ -0,0 +1,27 @@
+/**
+ * requirement: return result in linear time (O(n))
+ */
+function longestConsecutive(nums: number[]): number {
+  if (nums.length === 0) return 0;
+
+  const numSet = new Set(nums); // O(1) lookups
+  let maxLength = 0;
+
+  for (const num of numSet) {
+    // key: determine the "start" of a consecutive sequence.
+    // approach: if num - 1 doesn't exist in the set → num is the start of a sequence.
+    if (!numSet.has(num - 1)) {
+      let currentNum = num;
+      let currentLength = 1;
+
+      // count consecutive numbers
+      while (numSet.has(currentNum + 1)) {
+        currentNum++;
+        currentLength++;
+      }
+
+      maxLength = Math.max(maxLength, currentLength);
+    }
+  }
+  return maxLength;
+}

From 52742bd7b3c03b69a1b366d20dcce240583ee3bc Mon Sep 17 00:00:00 2001
From: Nancy Lee <saeryounglee@gmail.com>
Date: Fri, 25 Jul 2025 23:54:16 +0900
Subject: [PATCH 5/5] house robber solution

---
 house-robber/nancyel.ts | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 house-robber/nancyel.ts

diff --git a/house-robber/nancyel.ts b/house-robber/nancyel.ts
new file mode 100644
index 000000000..16bb0b073
--- /dev/null
+++ b/house-robber/nancyel.ts
@@ -0,0 +1,22 @@
+/**
+ * time complexity: O(n) - iterate over a loop
+ * space complexity: O(n) - dp array
+ *
+ * comment: initial naive implementation: simple odd/even alternation, which may return result that is "accidentally correct."
+ */
+function rob(nums: number[]): number {
+  // early return
+  if (nums.length === 0) return 0;
+  if (nums.length === 1) return nums[0];
+
+  const dp: number[] = new Array(nums.length);
+  dp[0] = nums[0];
+  dp[1] = Math.max(nums[0], nums[1]);
+
+  for (let i = 2; i < nums.length; i++) {
+    // select either 1) current + best from 2 houses ago or 2) skip current, best from previous
+    dp[i] = Math.max(nums[i] + dp[i - 2], dp[i - 1]);
+  }
+
+  return dp[nums.length - 1]; // max money from all houses
+}