Given a m x n 2D binary array grid which represents of map of '1's (land) and '0's (water), return the number of islands in this grid.

Given a 2D m x n array grid containing only 1s (land) and 0s (water), count the number of islands in it. An island is surrounded by

Given an array of positive integers nums and a positive number target, find the length of the smallest contiguous subarray whose sum is

Given an array of positive numbers and a positive number 'k', find the maximum sum of any contiguous subarray of size 'k'.