Two Pointers

Check palindrome ignoring non-alphanumeric.

On an n x n chessboard, a knight starts at the cell (row, column) and attempts to make exactly k moves. The rows and columns are 0-indexed, so the top-left cell is (0, 0), and the bottom-r

Given a 2D grid consists of 0s (land) and 1s (water). An _island_ is a maximal 4-directionally connected group of 0s and a _closed island_ is an island totally (all left, top, right, botto

You are given a circle represented as (radius, xCenter, yCenter) and an axis-aligned rectangle represented as (x1, y1, x2, y2), where (x1, y1) are the coordinates of the bottom-left corner, and

Two sum on sorted array, 1-indexed.

Find all unique triplets summing to zero.

Find two lines forming max water container.

Compute trapped water from elevation map.