Determine if a 9×9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:
- Each row must contain the digits
- Each column must contain the digits
- Each of the 9
3x3sub-boxes of the grid must contain the digits
Sometimes we need a data structure, it can save and retrieve data rapidly. In lots of circumstances, a hashtable is our best choice. Hashtable is a complex dynamic data structure, in the best situation is saving and retrieving time complexity is O(1).
In this article, we don’t discuss the implementation of the hashtable, We only collect the problems of the hashtable.
Some problems suit for the hashtable, like problems related string, may also suit for array solution. We may choose an array to solve these problems, but we can also use hashtable either.
Problems and Solutions:
- 1. Two Sum (Java)
- 3. Longest Substring Without Repeating Characters
- 30. Substring with Concatenation of All Words
- 36. Valid Sudoku
- 49. Group Anagrams
- 136. Single Number
- 202. Happy Number
- 205. Isomorphic Strings
- 217. Contains Duplicate
- 219. Contains Duplicate II
- 290. Word Pattern
- 299. Bulls and Cows
- 347. Top K Frequent Elements
- 349. Intersection of Two Arrays
- 350. Intersection of Two Arrays II
- 355. Design Twitter
Given two strings
T, return if they are equal when both are typed into empty text editors.
#means a backspace character.