Prefix-Sum

Problem You are given an array arr of positive integers. You are also given the array queries where queries[i] = [lefti, righti]. For each query i compute the XOR of elements from lefti to righti (that is, arr[lefti] XOR arr[lefti + 1] XOR ... XOR arr[righti] ). Return an array answer where answer[i] is the answer to the ith query. Examples Example 1: Input: arr = [1,3,4,8], queries = [ [0,1],[1,2],[0,3],[3,3] ] Output: [2,7,14,8] Explanation: The binary representation of the elements in the array are: 1 = 0001 3 = 0011 4 = 0100 8 = 1000 The XOR values for queries are: [0,1] = 1 xor 3 = 2 [1,2] = 3 xor 4 = 7 [0,3] = 1 xor 3 xor 4 xor 8 = 14 [3,3] = 8 ...

Problem There are n students in a class numbered from 0 to n - 1. The teacher will give each student a problem starting with the student number 0, then the student number 1, and so on until the teacher reaches the student number n - 1. After that, the teacher will restart the process, starting with the student number 0 again. You are given a 0-indexed integer array chalk and an integer k. There are initially k pieces of chalk. When the student number i is given a problem to solve, they will use chalk[i] pieces of chalk to solve that problem. However, if the current number of chalk pieces is strictly less than chalk[i], then the student number i will be asked to replace the chalk. ...

Problem Given an array of integers nums and an integer k. A continuous subarray is called nice if there are k odd numbers on it. Return the number of nice sub-arrays. Examples Example 1: Input: nums = [1,1,2,1,1], k = 3 Output: 2 Explanation: The only sub-arrays with 3 odd numbers are [1,1,2,1] and [1,2,1,1]. ...

Problem Given an array of integers arr. We want to select three indices i, j and k where (0 <= i < j <= k < arr.length). Let’s define a and b as follows: a = arr[i] ^ arr[i + 1] ^ ... ^ arr[j - 1] b = arr[j] ^ arr[j + 1] ^ ... ^ arr[k] Note that ^ denotes the bitwise-xor operation. ...

Problem Given an integer array nums and an integer k, return true if nums has a continuous subarray of size at least two whose elements sum up to a multiple of k, or false otherwise. An integer x is a multiple of k if there exists an integer n such that x = n * k. 0 is always a multiple of k. Examples Example 1: ...

Problem Given an array nums and a target value k, find the maximum length of a subarray that sums to k. If there isn’t one, return 0 instead. Note: The sum of the entire nums array is guaranteed to fit within the 32-bit signed integer range. Examples Example 1: Input: nums = [1, -1, 5, -2, 3], k = 3 Output: 4 Explanation: The subarray [1, -1, 5, -2] sums to 3 and is the longest. ...

`` Problem Given an array of integers nums and an integer k, return the total number of subarrays whose sum equals to k. Examples Example 1: Input: nums = [1,1,1], k = 2 Output: 2 Example 2: Input: nums = [1,2,3], k = 3 Output: 2 ...

Problem Given the root of a binary tree and an integer targetSum, return the number of paths where the sum of the values along the path equals targetSum. The path does not need to start or end at the root or a leaf, but it must go downwards (i.e., traveling only from parent nodes to child nodes). Examples Example 1: ...

Problem Given an integer array nums and an integer k, return the number of non-empty subarrays that have a sum divisible by k. A subarray is a contiguous part of an array. Examples Example 1: Input: nums = [4,5,0,-2,-3,1], k = 5 Output: 7 Explanation: There are 7 subarrays with a sum divisible by k = 5: [4, 5, 0, -2, -3, 1], [5], [5, 0], [5, 0, -2, -3], [0], [0, -2, -3], [-2, -3] ...

Problem Given an array of integers nums, calculate the pivot index of this array. The pivot index is the index where the sum of all the numbers strictly to the left of the index is equal to the sum of all the numbers strictly to the index’s right. If the index is on the left edge of the array, then the left sum is 0 because there are no elements to the left. This also applies to the right edge of the array. ...