1. 5x Balance a string with parentheses. "a(b)" -> "a(b)"; "(((((" -> ""; "(()())" -> "(()())"; ")ab(()" -> "ab()"; 
    etc...  + You have a string consisting of open and closed parentheses, but parentheses may be imbalanced.
2. 2x Given a 2D array of characters ('-' , 'X' , 'R' , 'T   '),
    find out whether there is a path from the robot 'R' to the target 'T'. 
    The robot can move up, down, left or right. 
    Cells marked with 'X' are blocked and cannot be passed through.
3. 5x Give tasks of diferrent kinds and a cooldown time. 
    Tasks of same kind must be separated by at least cooldown time to executed. 
    Write a program to detect conflicts in meeting schedules... 
    Given a schedule (array of start and end times) for meetings, provide an 
    algorithm that finds the minimum number of rooms needed for the day.    
4. 3x Do an in-place (without allocating any extra memory) rearrangement of a list of integers, 
    putting non-zero elements first. 
5. 6x Given Binary Tree is Binary Search tree or not.
6. 3x Given an array of integers find a contiguous subset that sums to a given number  
7. 3x Given a string break it up into meaningful sentence 
    "thesystemisrunning" => the system is running + Figure out how many words are in a string  
8. longest path in a tree regardless the directions? 
9. 2x Valid lottery number given string of digits
10. 2x find area of a room, 2D array, robot can move up down left right


Extra, probably google:
1. Parse a string containing numbers and "+", "-" and parentheses. Evaluate the expression.
2. You have a string of numbers, i.e. 123. 
    You can insert a + or - sign in front of ever number, or you can leave it empty. 
    Find all of the different possibilities, make the calculation and return the sum. 
    For example; +1+2+3 = 6 +12+3 = 15 +123 = 123 +1+23 = 24 ... -1-2-3 = 6 ... 
        Return the sum of all the results. 
3. variation of LCA problem  
4. Given two words and a dictionary, print the path from one word to the next 
    changing one letter at a time  
5. Given a list of chars, return the 2nd most frequently occurring char. 
6. Matrix of 0s and 1s, find left most 1
7. Find prime factors of number
8. mutiply two huge numbers one="98245092837409283720348029384" two="19823049823402938423"
9. Given %, ie. .4, find number in sorted array at position.
10. got get repeating decimal patter of division e.g. 1/3, 1/6
11. given n1, n2 is the same number after removing 1 digit. Given the sum n1+n2,
    find all possible values for n1,n2
12. given odd number print diamond pattern recursively
13. Store BST in list, then restore

1. 3x Print all permutations of a given string.  
2. merge two sorted linked lists  
3. Given an array of integers find the sum of k largest integers in that array.
4. Singly linked list. Print it backwards.
5. Search for an item in a sorted, but rotated, array.  
6. Permutation subsets 
7. 2x Coin DP problem
8. use bit operations to write a function that will determine if a number is a power of 2  
9. rotate a matrix 90 degrees clockwise  
10. Print a binary tree by column.  
11. Get digit - number of appearences of digit in array. i.e. 3 => {3, 13, 23, 30} = 4 times. 
    get digit - remove any number containing a digit. 
    get digit - return nth number
12. Can you use union to find detect cycle in directed graph
13. 3x Write fib iterator
14. In order successor of binary tree

1. Given the alphabet encoded as numbers (e.g., a=1, b=2, ..., z=26), 
    and a sequence of numbers (e.g., "23413259802"), 
    how many strings can be generated. 
2. Number pad combinations problem.
3. Given a million a million integers find the kth smallest  
4. Output a substring with at most k unique characters.
    "aabc" and k=2 -> "aab"  
5. Wildcard Pattern recognition  + match a regular expression to a string.