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 […]

Range Sum Query 2D – Immutable Given a 2D matrix matrix, find the sum of the elements inside the rectangle defined by (row1, col1), (row2, col2). Example: Given matrix = [ [3, 0, 1, 4, 2], [5, 6, 3, 2, 1], [1, 2, 0, 1, 5], [4, 1, 0, 1, […]

Factor Combinations Numbers can be regarded as product of its factors. For example, 8 = 2 x 2 x 2; = 2 x 4. Write a function that takes an integer n and return all possible combinations of its factors. Note: Each combination’s factors must be sorted ascending, for example: […]

Given an array of numbers nums, in which exactly two elements appear only once and all the other elements appear exactly twice. Find the two elements that appear only once. For example: Given nums = [1, 2, 1, 3, 2, 5], return [3, 5]. Note: The order of the result […]

Range Sum Query – Immutable Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive. Example: Given nums = [-2, 0, 3, -5, 2, -1] sumRange(0, 2) -> 1 sumRange(2, 5) -> -1 sumRange(0, 5) -> -3 Note: You may […]

Smallest Rectangle Enclosing Black Pixels An image is represented by a binary matrix with 0 as a white pixel and 1 as a black pixel. The black pixels are connected, i.e., there is only one black region. Pixels are connected horizontally and vertically. Given the location (x, y) of one […]

Remove Invalid Parentheses Remove the minimum number of invalid parentheses in order to make the input string valid. Return all possible results. Note: The input string may contain letters other than the parentheses ( and ). Examples: “()())()” -> [“()()()”, “(())()”] “(a)())()” -> [“(a)()()”, “(a())()”] “)(” -> [“”] Credits: Special […]

Longest Increasing Subsequence Given an unsorted array of integers, find the length of longest increasing subsequence. For example, Given [10, 9, 2, 5, 3, 7, 101, 18], The longest increasing subsequence is [2, 3, 7, 101], therefore the length is 4. Note that there may be more than one LIS […]