NeetCode Practice 150 -> Arrays & Hashing section completed

Author: Adrian333Dev

neetcode_practice_150/01_arrays-and-hashing/05_top-k-frequent-elements.js

@@ -4,4 +4,9 @@
  * @return {number[]}
  */
 const topKFrequent = (nums, k) => {
+	const repo = {};
+  for (let n of nums) repo[n] = (repo[n] || 0) + 1;
+  return Object.keys(repo).sort((a, b) => repo[b] - repo[a]).slice(0, k);
 };
+
+console.log(topKFrequent([1,1,1,2,2,3], 2));

neetcode_practice_150/01_arrays-and-hashing/06_product-of-array-except-self.js

@@ -0,0 +1,22 @@
+/**
+ * @param {number[]} nums
+ * @return {number[]}
+ */
+const productExceptSelf = (nums) => {
+	const productOfPrev = [nums[0]];
+	const productOfNext = [nums[nums.length - 1]];
+	for (let i = 1; i < nums.length; i++) {
+		productOfPrev.push(productOfPrev[i - 1] * nums[i]);
+		productOfNext.push(productOfNext[i - 1] * nums[nums.length - 1 - i]);
+	}
+	for (let i = 0; i < nums.length; i++)
+		nums[i] =
+			(i === 0 ? 1 : productOfPrev[i - 1]) *
+			(i === nums.length - 1 ? 1 : productOfNext[nums.length - 2 - i]);
+
+	return nums;
+};
+
+console.log(productExceptSelf([1, 2, 3, 4])); // [24,12,8,6]
+// console.log(productExceptSelf([-1, 1, 0, -3, 3])); // [0,0,9,0,0]
+// console.log(productExceptSelf([1, 2])); // [2,1]

neetcode_practice_150/01_arrays-and-hashing/07_valid-sudoku.js

@@ -0,0 +1,47 @@
+/**
+ * @param {character[][]} board
+ * @return {boolean}
+ */
+const isValidSudoku = (board) => {
+	let square = {};
+	for (let i = 0; i < 9; i++) {
+		let row = new Set();
+		for (let j = 0; j < 9; j++) {
+			const rowNum = board[i][j];
+			if (rowNum !== '.') {
+				const cellKey = `${Math.floor(i / 3)}-${Math.floor(j / 3)}`;
+				if (row.has(rowNum) || square[cellKey]?.has(rowNum)) return false;
+				else {
+					row.add(rowNum);
+					square[cellKey] = square[cellKey] || new Set();
+					square[cellKey].add(rowNum);
+				}
+			}
+		}
+	}
+
+	for (let i = 0; i < 9; i++) {
+		let col = new Set();
+		for (let j = 0; j < 9; j++) {
+			const colNum = board[j][i];
+			if (colNum !== '.' && col.has(colNum)) return false;
+			else col.add(colNum);
+		}
+	}
+
+	return true;
+};
+
+console.log(
+	isValidSudoku([
+		['5', '3', '.', '.', '7', '.', '.', '.', '.'],
+		['6', '.', '.', '1', '9', '5', '.', '.', '.'],
+		['.', '9', '8', '.', '.', '.', '.', '6', '.'],
+		['8', '.', '.', '.', '6', '.', '.', '.', '3'],
+		['4', '.', '.', '8', '.', '3', '.', '.', '1'],
+		['7', '.', '.', '.', '2', '.', '.', '.', '6'],
+		['.', '6', '.', '.', '.', '.', '2', '8', '.'],
+		['.', '.', '.', '4', '1', '9', '.', '.', '5'],
+		['.', '.', '.', '.', '8', '.', '.', '7', '9'],
+	])
+); // true

neetcode_practice_150/01_arrays-and-hashing/08_encode-and-decode-strings.js

@@ -0,0 +1,33 @@
+class Solution {
+	/*
+	 * @param strs: a list of strings
+	 * @return: encodes a list of strings to a single string.
+	 */
+	encode(strs) {
+		let result = '';
+		for (let str of strs) result += `<${str.length}>${str}`;
+		return result;
+	}
+
+	/*
+	 * @param str: A string
+	 * @return: dcodes a single string to a list of strings
+	 */
+	decode(str) {
+		let result = [];
+		let i = 0;
+		while (i < str.length) {
+			let j = str.indexOf('>', i);
+			let len = parseInt(str.slice(i + 1, j));
+      if (len > 0) result.push(str.slice(j + 1, j + len + 1));
+      i = j + len + 1;
+    }
+    return result;
+	}
+}
+
+const solution = new Solution();
+console.log(solution.encode(['lint', 'code', 'love', 'you'])); // <4>lint<4>code<4>love<3>you
+console.log(solution.decode('<4>lint<4>code<4>love<3>you')); // ['lint', 'code', 'love', 'you']
+console.log(solution.encode([''])); // <0>
+console.log(solution.decode('<0>')); // ['']

neetcode_practice_150/01_arrays-and-hashing/09_longest-consecutive-sequence.js

@@ -0,0 +1,21 @@
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+const longestConsecutive = (nums) => {
+	const bucket = new Set(nums);
+	let max = 0;
+	for (let n of nums) {
+		if (!bucket.has(n - 1)) {
+			let curr = n,
+				currLen = 1;
+			while (bucket.has(++curr)) currLen++;
+			max = Math.max(max, currLen);
+		}
+	}
+	return max;
+};
+
+console.log(longestConsecutive([100, 4, 200, 1, 3, 2])); // 4
+console.log(longestConsecutive([0, 3, 7, 2, 5, 8, 4, 6, 0, 1])); // 9
+console.log(longestConsecutive([1, 2, 0, 1])); // 3