1) Build Array from Permutations

Given an array (nums) of n positive integers (0 through n-1), build a new array (ans) of the same length where ans[i] = nums[nums[i]].

Input: nums = [0,2,1,5,3,4]
Output: [0,1,2,4,5,3]
Explanation: The array ans is built as follows: 
ans = [nums[nums[0]], nums[nums[1]], nums[nums[2]], nums[nums[3]], nums[nums[4]], nums[nums[5]]]
    = [nums[0], nums[2], nums[1], nums[5], nums[3], nums[4]]
    = [0,1,2,4,5,3]

Input: nums = [5,0,1,2,3,4]
Output: [4,5,0,1,2,3]
Explanation: The array ans is built as follows:
ans = [nums[nums[0]], nums[nums[1]], nums[nums[2]], nums[nums[3]], nums[nums[4]], nums[nums[5]]]
    = [nums[5], nums[0], nums[1], nums[2], nums[3], nums[4]]
    = [4,5,0,1,2,3]

2) Keyboard Rows

Keyboards have 3 rows of characters:

  • the first row consists of the characters “qwertyuiop”
  • the second row consists of the characters “asdfghjkl”
  • the third row consists of the characters “zxcvbnm”

Given an array of Strings, return an array of words that can be spelt with just one keyboard row.

Input: words = ["Hello","Alaska","Dad","Peace"]
Output: ["Alaska","Dad"]

Input: words = ["omk", "asdf"]
Output: ["asdf"]

3) Max Consecutive Ones

Given a binary array (nums), return the maxmum number of consecutives 1’s in the array.

Input: nums = [1,1,0,1,1,1]
Output: 3

Input: nums = [1,0,1,1,0,1]
Output: 2

4) Maximum Subarray

Given an integer array (nums), find the contiguous subarray) with the largest sum, and return its sum.

Input: nums = [-2,1,-3,4,-1,2,1,-5,4]
Output: 6
Explanation: [4,-1,2,1] has the largest sum = 6.

Input: nums = [1]
Output: 1

Input: nums = [5,4,-1,7,8]
Output: 23