[hyer0705] WEEK 05 solutions

best-time-to-buy-and-sell-stock/hyer0705.ts

@@ -0,0 +1,14 @@
+function maxProfit(prices: number[]): number {
+  let minPrice = Infinity;
+  let maxProfit = 0;
+
+  for (const price of prices) {
+    if (price < minPrice) {
+      minPrice = price;
+    } else {
+      maxProfit = Math.max(maxProfit, price - minPrice);
+    }
+  }
+
+  return maxProfit;
+}

encode-and-decode-strings/hyer0705.ts

@@ -0,0 +1,47 @@
+class Solution {
+  private DELIMITER = "*";
+
+  /**
+   * @param strs: a list of strings
+   * @returns: encodes a list of strings to a single string.
+   */
+  public encode(strs: string[]): string {
+    let encoded = "";
+
+    for (const str of strs) {
+      encoded += `${str.length}${this.DELIMITER}${str}`;
+    }
+
+    return encoded;
+  }
+
+  /**
+   * @param str: A string
+   * @returns: decodes a single string to a list of strings
+   */
+  public decode(str: string): string[] {
+    const decoded: string[] = [];
+
+    let stack: string[] = [];
+    let pointer = 0;
+
+    while (pointer < str.length) {
+      const char = str[pointer];
+
+      if (char === this.DELIMITER) {
+        let strLength: number = Number(stack.join(""));
+        stack = [];
+
+        const word = str.substring(pointer + 1, pointer + 1 + strLength);
+        pointer = pointer + 1 + strLength;
+
+        decoded.push(word);
+      } else {
+        stack.push(char);
+        pointer++;
+      }
+    }
+
+    return decoded;
+  }
+}

group-anagrams/hyer0705.ts

@@ -0,0 +1,15 @@
+function groupAnagrams(strs: string[]): string[][] {
+  const anagramsMap = new Map<string, string[]>();
+
+  for (const word of strs) {
+    const anagramKey = [...word].sort().join();
+
+    if (anagramsMap.has(anagramKey)) {
+      anagramsMap.get(anagramKey)!.push(word);
+    } else {
+      anagramsMap.set(anagramKey, [word]);
+    }
+  }
+
+  return Array.from(anagramsMap.values());
+}

implement-trie-prefix-tree/hyer0705.ts

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+class TNode {
+  isEndOf: boolean;
+  children: Map<string, TNode>;
+
+  constructor() {
+    this.isEndOf = false;
+    this.children = new Map<string, TNode>();
+  }
+}
+
+class Trie {
+  private root: TNode;
+
+  constructor() {
+    this.root = new TNode();
+  }
+
+  insert(word: string): void {
+    let currentNode: TNode = this.root;
+
+    for (const ch of word) {
+      if (currentNode.children.has(ch)) {
+        currentNode = currentNode.children.get(ch)!;
+      } else {
+        const newNode = new TNode();
+
+        currentNode.children.set(ch, newNode);
+        currentNode = currentNode.children.get(ch)!;
+      }
+    }
+    currentNode.isEndOf = true;
+  }
+
+  search(word: string): boolean {
+    let currentNode = this.root;
+
+    for (const ch of word) {
+      if (!currentNode.children.has(ch)) {
+        return false;
+      }
+
+      currentNode = currentNode.children.get(ch)!;
+    }
+
+    return currentNode.isEndOf;
+  }
+
+  startsWith(prefix: string): boolean {
+    let currentNode = this.root;
+
+    for (const ch of prefix) {
+      if (!currentNode.children.has(ch)) {
+        return false;
+      }
+
+      currentNode = currentNode.children.get(ch)!;
+    }
+
+    return true;
+  }
+}
+
+/**
+ * Your Trie object will be instantiated and called as such:
+ * var obj = new Trie()
+ * obj.insert(word)
+ * var param_2 = obj.search(word)
+ * var param_3 = obj.startsWith(prefix)
+ */

word-break/hyer0705.ts

@@ -0,0 +1,93 @@
+// using set
+function wordBreak(s: string, wordDict: string[]): boolean {
+  const sLen = s.length;
+
+  const dp: boolean[] = new Array(sLen + 1).fill(false);
+  dp[0] = true;
+
+  const wordSet = new Set<string>(wordDict);
+
+  for (let i = 1; i <= sLen; i++) {
+    for (let j = 0; j < i; j++) {
+      if (dp[j] && wordSet.has(s.substring(j, i))) {
+        dp[i] = true;
+        break;
+      }
+    }
+  }
+
+  return dp[sLen];
+}
+
+// using trie
+class TNode {
+  isEndOf: boolean;
+  children: Map<string, TNode>;
+
+  constructor() {
+    this.isEndOf = false;
+    this.children = new Map<string, TNode>();
+  }
+}
+
+class Trie {
+  root: TNode;
+
+  constructor() {
+    this.root = new TNode();
+  }
+
+  insert(word: string): void {
+    let currentNode = this.root;
+
+    for (const ch of word) {
+      if (!currentNode.children.has(ch)) {
+        currentNode.children.set(ch, new TNode());
+      }
+
+      currentNode = currentNode.children.get(ch)!;
+    }
+
+    currentNode.isEndOf = true;
+  }
+
+  search(word: string): boolean {
+    let currentNode = this.root;
+
+    for (const ch of word) {
+      if (!currentNode.children.has(ch)) {
+        return false;
+      }
+
+      currentNode = currentNode.children.get(ch)!;
+    }
+
+    return currentNode.isEndOf;
+  }
+}
+
+function wordBreak(s: string, wordDict: string[]): boolean {
+  const sLen = s.length;
+
+  const dp: boolean[] = new Array(sLen + 1).fill(false);
+  dp[0] = true;
+
+  const trie = new Trie();
+
+  for (const word of wordDict) {
+    trie.insert(word);
+  }
+
+  for (let i = 1; i <= sLen; i++) {
+    for (let j = 0; j < i; j++) {
+      if (dp[j]) {
+        if (trie.search(s.substring(j, i))) {
+          dp[i] = true;
+          break;
+        }
+      }
+    }
+  }
+
+  return dp[sLen];
+}