Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.

Given an integer n, count the total number of digit 1 appearing in all non-negative integers less than or equal to n.

Given two numbers represented as strings, return multiplication of the numbers as a string.

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add...

Write an algorithm to determine if a number is "happy".

As you can see, calculations of 4 × 3 and 6 × 2 are not necessary. Therefore, we only need to consider factors up to √n because, if n is divisible by some numbe...

Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.

Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array.

Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path.