Merge pull request #855 from choidabom/main

[choidabom] Week 5

Author: TonyKim9401

best-time-to-buy-and-sell-stock/choidabom.ts

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+/**
+ * https://leetcode.com/problems/best-time-to-buy-and-sell-stock/description/
+ * Runtime: 6ms, Memory: 62.30MB
+ *
+ * Time Complexity: O(N)
+ * Space Complexity: O(1)
+ */
+
+function maxProfit(prices: number[]): number {
+  let buyingPrice = prices[0];
+  let profit = 0;
+
+  for (const price of prices) {
+    buyingPrice = Math.min(price, buyingPrice);
+    profit = Math.max(profit, price - buyingPrice);
+  }
+
+  return profit;
+}
+
+maxProfit([7, 1, 5, 3, 6, 4]);

encode-and-decode-strings/choidabom.ts

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+/**
+ * https://www.lintcode.com/problem/659/
+ * Time Complexity: O(n)
+ * Space Complexity: O(n)
+ */
+
+function encode(strs: string[]): string {
+  return strs.join("😀");
+}
+
+function decode(str: string): string[] {
+  return str.split("😀");
+}
+
+decode(encode(["Hello", "World"]));
+/*
+ * output
+ * ["Hello","World"]
+ */

group-anagrams/choidabom.ts

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+/**
+ * https://leetcode.com/problems/group-anagrams/description/
+ * Runtime: 27ms, Memory: 64.26MB
+ *
+ * Time Complexity: O(n * m * log m)
+ * Space Complexity: O(n * m)
+ *
+ * 접근
+ * anagrams 관계인 단어는 정렬 시 모두 동일한 단어가 된다.
+ * 그러므로 정렬된 단어가 key 값이 되고, str을 정렬했을 때 key값과 동일한 경우 value가 되도록 추가.
+ */
+
+function groupAnagrams(strs: string[]): string[][] {
+  let answer = [];
+  const anagramMap = new Map<string, string[]>();
+
+  for (let str of strs) {
+    const key = str.split("").sort().join(""); // O(m * log m)
+    if (!anagramMap.has(key)) {
+      anagramMap.set(key, []);
+    }
+    anagramMap.get(key)?.push(str);
+  }
+
+  anagramMap.forEach((value) => {
+    answer.push(value);
+  });
+
+  return answer;
+}
+
+groupAnagrams(["eat", "tea", "tan", "ate", "nat", "bat"]);