Easy

1441. Build an Array With Stack Operations Given an array target and an integer n. In each iteration, you will read a number from list = {1,2,3…, n}. Build the target array using the following operations: Push: Read a new element from the beginning list, and push it in the array. Pop: delete the last element of the array. If the target array is already built, stop reading more elements. Return the operations to build the target array. You are guaranteed that the answer is unique. ...

1876. Substrings of Size Three with Distinct Characters A string is good if there are no repeated characters. Given a string s​​​​​, return the number of good substrings of length three in s​​​​​​. Note that if there are multiple occurrences of the same substring, every occurrence should be counted. A substring is a contiguous sequence of characters in a string. Example 1: Input: s = "xyzzaz" Output: 1 Explanation: There are 4 substrings of size 3: "xyz", "yzz", "zza", and "zaz". The only good substring of length 3 is "xyz". Example 2: Input: s = "aababcabc" Output: 4 Explanation: There are 7 substrings of size 3: "aab", "aba", "bab", "abc", "bca", "cab", and "abc". The good substrings are "abc", "bca", "cab", and "abc". Constraints: ...

1878. Get Biggest Three Rhombus Sums in a Grid You are given an m x n integer matrix grid​​​. A rhombus sum is the sum of the elements that form the border of a regular rhombus shape in grid​​​. The rhombus must have the shape of a square rotated 45 degrees with each of the corners centered in a grid cell. Below is an image of four valid rhombus shapes with the corresponding colored cells that should be included in each rhombus sum: ...

938. Range Sum of BST Given the root node of a binary search tree and two integers low and high, return the sum of values of all nodes with a value in the inclusive range [low, high]. Example 1: Input: root = [10,5,15,3,7,null,18], low = 7, high = 15 Output: 32 Explanation: Nodes 7, 10, and 15 are in the range [7, 15]. 7 + 10 + 15 = 32. ...

1859. Sorting the Sentence A sentence is a list of words that are separated by a single space with no leading or trailing spaces. Each word consists of lowercase and uppercase English letters. A sentence can be shuffled by appending the 1-indexed word position to each word then rearranging the words in the sentence. For example, the sentence “This is a sentence” can be shuffled as “sentence4 a3 is2 This1” or “is2 sentence4 This1 a3”. Given a shuffled sentence s containing no more than 9 words, reconstruct and return the original sentence. ...

1861. Rotating the Box You are given an m x n matrix of characters box representing a side-view of a box. Each cell of the box is one of the following: A stone ‘#’ A stationary obstacle ‘*’ Empty ‘.’ The box is rotated 90 degrees clockwise, causing some of the stones to fall due to gravity. Each stone falls down until it lands on an obstacle, another stone, or the bottom of the box. Gravity does not affect the obstacles’ positions, and the inertia from the box’s rotation does not affect the stones’ horizontal positions. ...

746. Min Cost Climbing Stairs You are given an integer array cost where cost[i] is the cost of ith step on a staircase. Once you pay the cost, you can either climb one or two steps. You can either start from the step with index 0, or the step with index 1. Return the minimum cost to reach the top of the floor. Example 1: Input: cost = [10,15,20] Output: 15 Explanation: Cheapest is: start on cost[1], pay that cost, and go to the top. Example 2: Input: cost = [1,100,1,1,1,100,1,1,100,1] Output: 6 Explanation: Cheapest is: start on cost[0], and only step on 1s, skipping cost[3]. Constraints: ...

66. Plus One Given a non-empty array of decimal digits representing a non-negative integer, increment one to the integer. The digits are stored such that the most significant digit is at the head of the list, and each element in the array contains a single digit. You may assume the integer does not contain any leading zero, except the number 0 itself. Example 1: Input: digits = [1,2,3] Output: [1,2,4] Explanation: The array represents the integer 123. Example 2: Input: digits = [4,3,2,1] Output: [4,3,2,2] Explanation: The array represents the integer 4321. Example 3: Input: digits = [0] Output: [1] Constraints: ...

1342. Number of Steps to Reduce a Number to Zero Given a non-negative integer num, return the number of steps to reduce it to zero. If the current number is even, you have to divide it by 2, otherwise, you have to subtract 1 from it. Example 1: Input: num = 14 Output: 6 Explanation: Step 1) 14 is even; divide by 2 and obtain 7. Step 2) 7 is odd; subtract 1 and obtain 6. Step 3) 6 is even; divide by 2 and obtain 3. Step 4) 3 is odd; subtract 1 and obtain 2. Step 5) 2 is even; divide by 2 and obtain 1. Step 6) 1 is odd; subtract 1 and obtain 0. Example 2: Input: num = 8 Output: 4 Explanation: Step 1) 8 is even; divide by 2 and obtain 4. Step 2) 4 is even; divide by 2 and obtain 2. Step 3) 2 is even; divide by 2 and obtain 1. Step 4) 1 is odd; subtract 1 and obtain 0. Example 3: Input: num = 123 Output: 12 Solution class Solution { public int numberOfSteps(int num) { int count = 0; while (num != 0) { if (num % 2 == 0) { num = num / 2; } else { num-= 1; } count++; } return count; } }

1207. Unique Number of Occurrences Given an array of integers arr, write a function that returns true if and only if the number of occurrences of each value in the array is unique. Example 1: Input: arr = [1,2,2,1,1,3] Output: true Explanation: The value 1 has 3 occurrences, 2 has 2 and 3 has 1. No two values have the same number of occurrences. Example 2: Input: arr = [1,2] Output: false Example 3: Input: arr = [-3,0,1,-3,1,1,1,-3,10,0] Output: true Constraints: ...