[이병현] Week 1

contains-duplicate/tolluset.ts

@@ -0,0 +1,7 @@
+/*
+ * TC: O(n)
+ * SC: O(n)
+ * */
+function containsDuplicate(nums: number[]): boolean {
+  return nums.length !== new Set(nums).size;
+}

kth-smallest-element-in-a-bst/tolluset.ts

@@ -0,0 +1,42 @@
+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)
+ * SC: O(n)
+ * */
+function kthSmallest(root: TreeNode, k: number): number {
+  let count = 0;
+  let result: null | number = null;
+
+  const inOrder = (node: TreeNode | null) => {
+    if (!node || result !== null) {
+      return false;
+    }
+
+    if (inOrder(node.left)) {
+      return true;
+    }
+
+    count++;
+
+    if (count === k) {
+      result = node.val;
+      return true;
+    }
+
+    inOrder(node.right);
+  };
+
+  inOrder(root);
+
+  return result!;
+}

number-of-1-bits/tolluset.ts

@@ -0,0 +1,10 @@
+/*
+ * TC: O(logn)
+ * SC: O(logn)
+ * */
+function hammingWeight(n: number): number {
+  return n
+    .toString(2)
+    .split("")
+    .filter((s) => s === "1").length;
+}

palindromic-substrings/tolluset.ts

@@ -0,0 +1,43 @@
+/*
+ * TC: O(n)
+ * SC: O(n)
+ * */
+function countSubstrings(s: string): number {
+  const transformedString = "#" + s.split("").join("#") + "#";
+  const transformedStringLength = transformedString.length;
+  const palindromeLengths = new Array(transformedStringLength).fill(0);
+  let currentCenter = 0,
+    rightBoundary = 0,
+    totalPalindromeCount = 0;
+
+  for (let i = 0; i < transformedStringLength; i++) {
+    // If i is within the rightmost center, copy the palindromes value from the mirror
+    if (i < rightBoundary) {
+      palindromeLengths[i] = Math.min(
+        rightBoundary - i,
+        palindromeLengths[currentCenter * 2 - i],
+      );
+    }
+
+    // Expand around i until it's not a palindrome and not over left or right
+    while (
+      i + palindromeLengths[i] + 1 < transformedStringLength &&
+      i - palindromeLengths[i] - 1 >= 0 &&
+      transformedString[i + palindromeLengths[i] + 1] ===
+        transformedString[i - palindromeLengths[i] - 1]
+    ) {
+      palindromeLengths[i]++;
+    }
+
+    // If palindromes value is the new rightmost center, update center and right
+    if (i + palindromeLengths[i] > radius) {
+      currentCenter = i;
+      rightBoundary = i + palindromeLengths[i];
+    }
+
+    // Add the number of palindromes with center i to the result
+    total += Math.floor((palindromeLengths[i] + 1) / 2);
+  }
+
+  return total;
+}

top-k-frequent-elements/tolluset.ts

@@ -0,0 +1,26 @@
+type Nums = [number, number][];
+
+/*
+ * TC: O(nlogn)
+ * SC: O(n)
+ * */
+function topKFrequent(nums: number[], k: number): number[] {
+  const counting = (arr: number[]) =>
+    arr.reduce(
+      (acc, n) => acc.set(n, (acc.get(n) ?? 0) + 1),
+      new Map<number, number>(),
+    );
+
+  const toValues = (map: Map<number, number>) => Array.from(map.entries());
+
+  const sorting = (arr: Nums) => arr.sort((a, b) => b[1] - a[1]);
+
+  const getK = (arr: Nums, k: number) => arr.slice(0, k).map((v) => v[0]);
+
+  return pipe(counting, toValues, sorting, (arr: Nums) => getK(arr, k))(nums);
+}
+
+const pipe =
+  (...fns: Function[]) =>
+  (x: any) =>
+    fns.reduce((v, f) => f(v), x);