Robina Li

Rearrange nums such that nums[0] < nums[1] > nums[2] < nums[3] ... (wiggle order).

A parentheses string is valid if and only if:

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

Given a binary array nums, return the maximum length of a contiguous subarray with an equal number of 0 and 1.

The median is the middle value in an ordered integer list. If the size of the list is even, there is no middle value. So the median is the mean...

You are given an array of integers nums, there is a sliding window of size k which is moving from the very left of the array to the very right....

Given a binary array nums, return the maximum number of consecutive 1’s in the array.

Given an array nums of n integers, return an array of all the unique quadruplets [nums[a], nums[b], nums[c], nums[d]] such that:

Trees are one of the most frequently tested data structures in coding interviews. This page collects ready-to-use Java templates for every major tree pattern — from basic traversals to advanced...

Minimal, copy-paste Java for combinatorics (nCk mod P) and 2D geometry primitives (cross product, point on segment).