DagnyTagg2013

"""

PROBLEM:

  4-digit number:  2284
  - assume have dictionary isWord(String word)
  - assume have phonenum pad digit to set of letters
  - print all possible words of ANY length up to 4-digits 
  

DagnyTagg2013

"""

  Given String "ABC", print all 3-letter permutations of this
  
"""

# SOLUTION:  - FULL decision tree
#            - each level is character place, 
#              each branch a choice of one char
#            - REMAINING unchosen characters

DagnyTagg2013

#
# You have data for social network on who is friends with whom.
# You need to write a function that returns this data in the form of an adjacency list representation, i.e. a mapping of each employee ID to a list of his/her friends on the site
# #
# You have two input data sets to work with. The first data set is the employees at your company, and the second is all the pairs of employees who are virtually friends so far. It does not matter which employee's ID is in which column, the friendships are bidirectional.
#
# employees_input = [
#   "1,Richard,Engineering",
#   "2,Erlich,HR",
#   "3,Monica,Business",

DagnyTagg2013

"""

MATCH BRACKETS

"""

"""

BAM:  dynamic STACK - append opens, then match-pop on closes 
      DICT to match CLOSE to OPEN (as BACK-MATCH), 

DagnyTagg2013

# ATTN: import Q for BFS traversal 
# https://stackoverflow.com/questions/717148/queue-queue-vs-collections-deque
from collections import deque
# ATTN: import simplest DICT for Graph Adjacency list 
# https://stackoverflow.com/questions/5900578/how-does-collections-defaultdict-work
from collections import defaultdict
# ATTN:  import simplest COUNTER dictionary for Distance accum for EQUAL-weighted OCCURRENCE counts but LESS GENERAL-FLEXIBLE than adding VARIABLE edge weight using DefaultDict!
# https://pymotw.com/2/collections/counter.html
from collections import Counter
from sys import maxsize

DagnyTagg2013

"""
PROBLEM - Stack from two Queues
"""

"""

STACK - LIFO, I/O from the SAME, ONE side
      - tracks TOP
      - push/pop on TOP
QUEUE - FIFO, Input at END, Output from FRONT; from DIFFERENT, TWO sides

DagnyTagg2013

# Given:  1=>2=>3=>4=>5
# Write function that takes head of list, n=2, and returns node 4 where n is distance from end

# TRICK:  Need to traverse TWICE always in FORWARD direction
#         1) count index from 0 to LENGTH to find the END so we can calculate 
#            complement FORWARD distance!
#         2) traverse counting from 0 to (LENGTH - n) to return reference to node!

# CAREFUL:  => Need to handle out-of-bounds on BOTH LOWER, and HIGHER end List
#           and since this deals with (LENGTH - n), this translates to

DagnyTagg2013

"""

PROBLEM:  Implement MRU Cache 
- i.e. cache the MOST-MOST-RECENTLY-USED-OR-ACCESSED, and drop LEAST-RECENTLY-USED

- FIXED-size cache
initialized with a size, never to exceed that size
- put(key, val), O(1)
- get(key) -> val (or None), O(1)

DagnyTagg2013

# PROBLEM:  Count and Construct All Distinct Valid Paths Through a Maze

# TRICK0:  
# - mutable heap-allocated structure to accumulate results to
# - cross-recursion-level visibility
# - use TUPLE to group MUTABLE ELEMENTs for state accumulation
# - globalValidPathCounter as first item of mutable LIST
# - used as INDEX into globalValidPaths Dict

DagnyTagg2013

"""
DELETE node from Binary Tree

CORE CASES:
*** CAREFUL/INTERESTING
-- need to distinguish applicable SIDE(left or right child); INTO TARGET from  
PARENT, as well as OUT of TARGET
- target is root => reset root to None
- target has no child; and target is LEFT or RIGHT child of parent 
            => reset parent's child (specific side) to None