[byol-han] WEEK 01 solutions

contains-duplicate/byol-han.js

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+// Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.
+/**
+ * @param {number[]} nums
+ * @return {boolean}
+ */
+var containsDuplicate = function (nums) {
+  const uniqueSet = new Set(nums);
+  return uniqueSet.size !== nums.length;
+};

house-robber/byol-han.js

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+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var rob = function (nums) {
+  if (nums.length === 0) return 0;
+  if (nums.length === 1) return nums[0];
+
+  let dp = [];
+  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/byol-han.js

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+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var longestConsecutive = function (nums) {
+  if (nums.length === 0) return nums.length;
+
+  const setNums = new Set(nums);
+  const sortNums = [...setNums].sort((a, b) => a - b);
+
+  let longest = 1;
+  let currentlength = 1;
+
+  for (let i = 0; i < sortNums.length; i++) {
+    if (sortNums[i] + 1 === sortNums[i + 1]) {
+      currentlength++;
+      longest = Math.max(longest, currentlength);
+    } else {
+      currentlength = 1;
+    }
+  }
+  return longest;
+};

top-k-frequent-elements/byol-han.js

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+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number[]}
+ */
+var topKFrequent = function (nums, k) {
+  const freqMap = new Map();
+
+  // 빈도수 계산
+  for (const num of nums) {
+    freqMap.set(num, (freqMap.get(num) || 0) + 1);
+  }
+
+  // Min Heap을 사용해서 상위 k개만 유지
+  return Array.from(freqMap.entries()) // [ [num, count], [num, count], ... ]
+    .sort((a, b) => b[1] - a[1]) // 빈도수를 기준으로 내림차순 정렬
+    .slice(0, k) // 상위 k개 선택
+    .map((entry) => entry[0]); // 숫자만 추출
+
+  return result;
+};

two-sum/byol-han.js

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+// Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
+
+// You may assume that each input would have exactly one solution, and you may not use the same element twice.
+
+// You can return the answer in any order.
+
+/**
+ * @param {number[]} nums
+ * @param {number} target
+ * @return {number[]}
+ */
+var twoSum = function (nums, target) {
+  let result = [];
+  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 result;
+};