[choidabom] WEEK 01 solutions

contains-duplicate/choidabom.ts

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+// https://leetcode.com/problems/contains-duplicate/description/
+
+// TC: O(n)
+// SC: O(n)
+
+function containsDuplicate(nums: number[]): boolean {
+  const set = new Set(nums);
+  return set.size !== nums.length;
+}
+
+function containsDuplicate(nums: number[]): boolean {
+  const set = new Set();
+
+  for (const num of nums) {
+    if (set.has(num)) {
+      return true;
+    }
+    set.add(num);
+  }
+
+  return false;
+}
+
+console.log(containsDuplicate([1, 1, 1, 3, 3, 4, 3, 2, 4, 2]));

house-robber/choidabom.ts

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+// https://leetcode.com/problems/house-robber/
+
+// TC: O(n)
+// SC: O(n)
+
+function rob(nums: number[]): number {
+  if (nums.length === 1) return nums[0];
+  if (nums.length === 2) return Math.max(nums[0], nums[1]);
+
+  const dp: number[] = [];
+  dp[0] = nums[0];
+  dp[1] = Math.max(nums[0], nums[1]);
+
+  for (let i = 2; i < nums.length; i++) {
+    dp[i] = Math.max(dp[i - 1], dp[i - 2] + nums[i]);
+  }
+
+  return dp[nums.length - 1];
+}

longest-consecutive-sequence/choidabom.ts

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+// https://leetcode.com/problems/longest-consecutive-sequence/
+
+// TC: O(n)
+// SC: O(n)
+
+function longestConsecutive(nums: number[]): number {
+  const numSet = new Set(nums);
+  let maxLen = 0;
+
+  for (const num of numSet) {
+    if (!numSet.has(num - 1)) {
+      let currentNum = num;
+      let length = 1;
+
+      while (numSet.has(currentNum + 1)) {
+        currentNum += 1;
+        length += 1;
+      }
+
+      maxLen = Math.max(maxLen, length);
+    }
+  }
+
+  return maxLen;
+}

top-k-frequent-elements/choidabom.ts

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+// https://leetcode.com/problems/top-k-frequent-elements/
+
+// TC: O(nlogn)
+// SC: O(n)
+
+function topKFrequent(nums: number[], k: number): number[] {
+  const map = new Map();
+
+  for (const num of nums) {
+    if (map.has(num)) {
+      map.set(num, map.get(num) + 1);
+    } else {
+      map.set(num, 1);
+    }
+  }
+
+  const sortedMap = [...map].sort((a, b) => b[1] - a[1]);
+  return sortedMap.splice(0, k).map((item) => item[0]);
+}

two-sum/choidabom.ts

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+// https://leetcode.com/problems/two-sum/
+
+// TC: O(n^2)
+// SC: O(1)
+
+function twoSum(nums: number[], target: number): number[] {
+  for (let i = 0; i < nums.length; i++) {
+    for (let j = i + 1; j < nums.length; j++) {
+      if (nums[i] + nums[j] === target) {
+        return [i, j];
+      }
+    }
+  }
+  return [];
+}
+
+// TC: O(n)
+// SC: O(n)
+
+function twoSum(nums: number[], target: number): number[] {
+  const map = new Map();
+
+  for (let i = 0; i < nums.length; i++) {
+    const num = nums[i];
+    const diff = target - num;
+
+    if (map.has(diff)) {
+      return [i, map.get(diff)];
+    } else {
+      map.set(num, i);
+    }
+  }
+  return [];
+}
+
+console.log(twoSum([2, 7, 11, 15], 9));