Given an integer n, count the total number of digit 1 appearing in all non-negative integers less than or equal to n. For example: Given n = 13, Return 6, because digit 1 occurred in the following numbers: 1, 10, 11, 12, 13. Brute force solution o(n) in time, TLE. […]
Palindrome Linked List Given a singly linked list, determine if it is a palindrome. Follow up: Could you do it in O(n) time and O(1) space? O(n) time, O(n)space solution, use a stack. /** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * […]
Delete Node in a Linked List Write a function to delete a node (except the tail) in a singly linked list, given only access to that node. Supposed the linked list is 1 -> 2 -> 3 -> 4 and you are given the third node with value 3, the […]
Read N Characters Given Read4 The API: int read4(char *buf) reads 4 characters at a time from a file. The return value is the actual number of characters read. For example, it returns 3 if there is only 3 characters left in the file. By using the read4 API, implement […]
Number of Islands II A 2d grid map of m rows and n columns is initially filled with water. We may perform an addLand operation which turns the water at position (row, col) into a land. Given a list of positions to operate, count the number of islands after each […]
Product of Array Except Self Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i]. Solve it without division and in O(n). For example, given [1,2,3,4], return [24,12,8,6]. Follow […]
Search a 2D Matrix II Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties: Integers in each row are sorted in ascending from left to right. Integers in each column are sorted in ascending from top to bottom. […]
Strobogrammatic Number III A strobogrammatic number is a number that looks the same when rotated 180 degrees (looked at upside down). Write a function to count the total strobogrammatic numbers that exist in the range of low <= num <= high. For example, Given low = “50”, high = “100”, […]
Group Shifted Strings Given a string, we can “shift” each of its letter to its successive letter, for example: “abc” -> “bcd”. We can keep “shifting” which forms the sequence: “abc” -> “bcd” -> … -> “xyz” Given a list of strings which contains only lowercase alphabets, group all strings […]
Different Ways to Add Parentheses Given a string of numbers and operators, return all possible results from computing all the different possible ways to group numbers and operators. The valid operators are+, – and *. Example 1 Input: “2-1-1”. ((2-1)-1) = 0 (2-(1-1)) = 2 Output: [0, 2] Example 2 […]