Merge pull request #370 from tolluset/main

[이병현] Week 2

Author: DaleSeo

construct-binary-tree-from-preorder-and-inorder-traversal/tolluset.ts

@@ -0,0 +1,36 @@
+class TreeNode {
+  val: number;
+  left: TreeNode | null;
+  right: TreeNode | null;
+  constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+    this.val = val === undefined ? 0 : val;
+    this.left = left === undefined ? null : left;
+    this.right = right === undefined ? null : right;
+  }
+}
+
+/**
+ *  TC: O(n^2)
+ *  SC: O(n)
+ * */
+function buildTree(preorder: number[], inorder: number[]): TreeNode | null {
+  if (!preorder?.length || !inorder?.length) {
+    return null;
+  }
+
+  const rootValue = preorder[0];
+  const root = new TreeNode(rootValue);
+  const inorderRootIndex = inorder.indexOf(rootValue);
+
+  root.left = buildTree(
+    preorder.slice(1, inorderRootIndex + 1),
+    inorder.slice(0, inorderRootIndex),
+  );
+
+  root.right = buildTree(
+    preorder.slice(inorderRootIndex + 1),
+    inorder.slice(inorderRootIndex + 1),
+  );
+
+  return root;
+}

counting-bits/tolluset.ts

@@ -0,0 +1,13 @@
+/*
+ * TC: O(nlogn)
+ * SC: O(nlogn)
+ * */
+function countBits(n: number): number[] {
+  return Array.from({ length: n + 1 }, (_, i) => i).map(
+    (v) =>
+      v
+        .toString(2)
+        .split("")
+        .filter((v) => v === "1").length,
+  );
+}

decode-ways/tolluset.ts

@@ -0,0 +1,26 @@
+/**
+ * TC: O(n)
+ * SC: O(n)
+ */
+function numDecodings(s: string): number {
+  const n = s.length;
+  const dp = new Array(n + 1).fill(0);
+
+  dp[0] = 1;
+  dp[1] = Number(s[0]) === 0 ? 0 : 1;
+
+  for (let i = 2; i <= n; i++) {
+    const oneDigit = Number(s.slice(i - 1, i));
+    const twoDigits = Number(s.slice(i - 2, i));
+
+    if (oneDigit >= 1 && oneDigit <= 9) {
+      dp[i] += dp[i - 1];
+    }
+
+    if (twoDigits >= 10 && twoDigits <= 26) {
+      dp[i] += dp[i - 2];
+    }
+  }
+
+  return dp[n];
+}

encode-and-decode-strings/tolluset.ts

@@ -0,0 +1,11 @@
+/*
+ * TC: O(nm)
+ * SC: O(nm)
+ * */
+function encode(arr: string[]): string {
+  return arr.join("🎃");
+}
+
+function decode(str: string): string[] {
+  return str.split("🎃");
+}

valid-anagram/tolluset.ts

@@ -0,0 +1,17 @@
+/*
+ * TC: O(n)
+ * SC: O(n)
+ * */
+function isAnagram(s: string, t: string): boolean {
+  if (s.length !== t.length) {
+    return false;
+  }
+
+  const groupS = groupBy(s);
+  const groupT = groupBy(t);
+
+  return Object.keys(groupS).every((k) => groupS[k] === groupT[k]);
+}
+
+const groupBy = (v: string) =>
+  v.split("").reduce((acc, cur) => ((acc[cur] = (acc[cur] ?? 0) + 1), acc), {});