Robina Li

Tic-tac-toe is played on a 3 x 3 grid by two players A and B. Player A always plays first. Given an array moves where moves[i] = [row, col] indicates...

Given a positive integer n, generate an n × n matrix filled with elements from 1 to n² in spiral order (clockwise).

Given two non-negative integers represented as strings num1 and num2, return their product as a string. You cannot convert the inputs to integers directly (numbers can be very large).

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.

The count-and-say sequence is a sequence of digit strings defined by the recursive formula:

You are given an array of k linked lists, each sorted in ascending order. Merge all the linked lists into one sorted linked list and return it.

Two strings are special-equivalent if you can swap characters at even indices among themselves and swap characters at odd indices among themselves, any number of times. Return the number of...

Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

Given two integers dividend and divisor, divide two integers without using multiplication, division, and mod operator. Return the quotient after dividing dividend by divisor. The integer division should truncate toward...

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