DaleStudy · TonyKim9401 · Jan 12, 2025 · Jan 6, 2025 · Jan 9, 2025 · Jan 9, 2025
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+/**
+ * 121. Best Time to Buy and Sell Stock
+ * You are given an array prices where prices[i] is the price of a given stock on the ith day.
+ * You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.
+ * Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return 0.
+ *
+ * https://leetcode.com/problems/best-time-to-buy-and-sell-stock/description/
+ */
+
+// O(n) time
+// O(1) space
+function maxProfit(prices: number[]): number {
+  let highestProfit = 0;
+  let left = 0;
+  let right = 1;
+
+  while (right < prices.length) {
+    if (prices[left] < prices[right]) {
+      let profit = prices[right] - prices[left];
+      highestProfit = Math.max(highestProfit, profit);
+    } else {
+      left = right;
+    }
+
+    right++;
+  }
+
+  return highestProfit;
+}
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+/**
+ * 659 · Encode and Decode Strings
+ * Design an algorithm to encode a list of strings to a string. The encoded string is then sent over the network and is decoded back to the original list of strings.
+ * Please implement encode and decode
+ *
+ * https://leetcode.com/problems/encode-and-decode-strings/description/
+ * https://www.lintcode.com/problem/659/
+ *
+ */
+
+// O(n) time
+// O(1) space
+function encode(strs: string[]): string {
+  let result = "";
+
+  for (const str of strs) {
+    result += `${str.length}#${str}`;
+  }
+
+  return result;
+}
+
+// O(n) time
+// O(n) space
+function decode(str: string) {
+  const result: string[] = [];
+
+  let i = 0;
+  while (i < str.length) {
+    let pos = str.indexOf("#", i);
+    const len = Number(str.slice(i, pos));
+    const word = str.slice(pos + 1, pos + 1 + len);
+    result.push(word);
+    i = pos + 1 + len;
+  }
+
+  return result;
+}
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+/**
+ * 49. Group Anagrams
+ * Given an array of strings strs, group the anagrams together. You can return the answer in any order.
+ *
+ * https://leetcode.com/problems/group-anagrams/description/
+ */
+
+// O(n * mlog(m)) time
+// O(n) space
+function groupAnagrams(strs: string[]): string[][] {
+  const result: string[][] = [];
+  const map = new Map<string, string[]>();
+
+  for (let i = 0; i < strs.length; i++) {
+    const word = strs[i];
+    const sorted = word.split("").sort().join("");
+
+    if (map.has(sorted)) {
+      map.get(sorted)!.push(word);
+    } else {
+      map.set(sorted, [word]);
+    }
+  }
+
+  map.forEach((v) => result.push(v));
+
+  return result;
+}