added exercises

Author: CheezItMan

README.md

@@ -1 +1,85 @@
-# hash-practice
+# Hash Table Practice
+
+In this exercise you will complete two coding problems using Hash Tables.
+
+## Learning Goals
+
+By the end of this exercise you should be able to:
+
+- Use a hash table to solve a coding problem
+- Identify how a hash table can produce a more attractive runtime over alternative solutions
+
+## Grouped Anagrams
+
+Given an array of strings, group anagrams together.
+
+### Example
+
+```
+Input: ["eat", "tea", "tan", "ate", "nat", "bat"],
+Output:
+[
+  ["ate","eat","tea"],
+  ["nat","tan"],
+  ["bat"]
+]
+```
+
+Note:
+
+- All inputs will be in lowercase.
+- The order of your output does not matter
+
+## Valid Sudoku
+
+Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:
+
+1. Each row must contain the digits 1-9 without repetition.
+1. Each column must contain the digits 1-9 without repetition.
+1. Each of the 9 3x3 sub-boxes of the grid must contain the digits 1-9 without repetition.
+
+![sudoku image](images/250px-Sudoku-by-L2G-20050714.svg.png)
+
+Above is a valid Sudoku grid.
+
+The Sudoku board could be partially filled, where empty cells are filled with the character '.'.
+
+**Example 1:**
+
+```
+Input:
+[
+  ["5","3",".",".","7",".",".",".","."],
+  ["6",".",".","1","9","5",".",".","."],
+  [".","9","8",".",".",".",".","6","."],
+  ["8",".",".",".","6",".",".",".","3"],
+  ["4",".",".","8",".","3",".",".","1"],
+  ["7",".",".",".","2",".",".",".","6"],
+  [".","6",".",".",".",".","2","8","."],
+  [".",".",".","4","1","9",".",".","5"],
+  [".",".",".",".","8",".",".","7","9"]
+]
+Output: true
+```
+
+
+**Example 2:**
+
+```
+Input:
+[
+  ["8","3",".",".","7",".",".",".","."],
+  ["6",".",".","1","9","5",".",".","."],
+  [".","9","8",".",".",".",".","6","."],
+  ["8",".",".",".","6",".",".",".","3"],
+  ["4",".",".","8",".","3",".",".","1"],
+  ["7",".",".",".","2",".",".",".","6"],
+  [".","6",".",".",".",".","2","8","."],
+  [".",".",".","4","1","9",".",".","5"],
+  [".",".",".",".","8",".",".","7","9"]
+]
+Output: false
+Explanation: Same as Example 1, except with the 5 in the top left corner being 
+    modified to 8. Since there are two 8's in the top left 3x3 sub-box, it is invalid.
+
+```