Robina Li

Given an integer n, return the number of structurally unique BST’s (binary search trees) that have exactly n nodes with values from 1 to n.

Given a string s, partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s.

This is a classic backtracking problem that requires generating all possible combinations of k numbers chosen from the range [1, n]. The key insight is using DFS with backtracking to...

An n-bit gray code sequence is a sequence of 2^n integers where:

Given an m x n matrix, return all elements of the matrix in spiral order.

Implement pow(x, n), which calculates x raised to the power n (i.e., x^n).

This is a classic dynamic programming problem that requires finding the number of unique paths from top-left to bottom-right of a grid. The key insight is recognizing the overlapping subproblems...

This is a complex linked list problem that requires reversing nodes in groups of k. The key insight is using recursion to handle the grouping and a helper function to...

This is a matrix manipulation problem that requires rotating a 2D matrix 90 degrees clockwise in-place. The key insight is understanding the relationship between matrix positions during rotation and implementing...

This is a classic stack problem that requires evaluating mathematical expressions written in Reverse Polish Notation (RPN). The key insight is using a stack to process operands and operators in...