example interview problems

# Problem 1 (easy): first unique character in a string
input_string = 'treetraversal'
output = 'v'

# Answer
def first_unique(input_string):
    count_map = {}
    for letter in input_string:
        if letter not in count_map:
            count_map[letter] = 1
        else:
            count_map[letter] += 1
    for letter in input_string:
        if count_map[letter] == 1:
            return letter
        
print(first_unique(input_string))

# Problem 2 (easy): Group Anagrams
entries = ['star', 'astr', 'car', 'rac', 'st']
output = [['star', 'astr'], ['car', 'rac'], ['st']]

# Answer
def group_anagrams(entries):
    anagram_map = {}
    for entry in entries:
        sorted_entry = ''.join(sorted(entry))
        if sorted_entry not in anagram_map:
            anagram_map[sorted_entry] = [entry]
        else:
            anagram_map[sorted_entry].append(entry)
    return anagram_map.values()
        
print(group_anagrams(entries))

# Problem 3 (medium): Design a OOP class for imaginary number arithmetic
# Notes that (write this out in math term on the whiteboard)
# a + b = (a.r + b.r) + (a.i + b.i)i
# a - b = (a.r - b.r) + (a.i - b.i)i

class Complex(object):
    
    def __init__(self, r, i):
        self.r = r
        self.i = i

def __str__(self):
        '''Returns complex number as a string'''
        return '%s + %si' % (self.r, self.i)

def __add__(self, other):
        '''Adds complex numbers'''
        return Complex(self.r + other.r, self.i + other.i)

def __sub__(self, other):
        '''Adds complex numbers'''
        return Complex(self.r - other.r, self.i - other.i)
    
    def __mul__(self, other):
        '''Multiplies numbers: Provide this (ac - bd) + (ad + bc)i'''
        return Complex(
        	self.r * other.r - self.i * other.i,
            self.i * other.r - self.r * other.i,
        )
    
    def __abs__(self):
        '''absolute value of self'''
        return (self.r**2 + self.i**2)**0.5

a = Complex(1, 2)
b = Complex(2, 3)
print(a)
print(b)
print(a + b)
print(a - b)
print(a * b)
print(abs(a))

# Problem 4 (SQL):
# Given a table (name, component, salary) with sample records:
# chris, bonus, 1000
# chris, bonus, 500 (there can be multiple entries for bonuses)
# chris, base, 10000
# adam, bonus, 5000
# adam, bonus, 50
# adam, base, 30000
# ...
# Write SQL to return result as (name, bonus_salary, base_salary)
#
# Answer
# SELECT
#   name,
#    SUM(CASE WHEN component = "bonus" THEN salary ELSE 0 END) AS "bonus_salary"
#    SUM(CASE WHEN component = "base" THEN salary ELSE 0 END) AS "base_salary"
# FROM table
# GROUP BY name;
#
# How would you do this in a scripting language e.g. Python.  You may assume records is array<Map<string, mixed>>
#
# Solution:
data = [
  {'name': 'chris', 'component': 'bonus', 'salary': 1000},
  {'name': 'chris', 'component': 'bonus', 'salary': 500},
  {'name': 'chris', 'component': 'base', 'salary': 10000},
  {'name': 'adam', 'component': 'bonus', 'salary': 5000},
  {'name': 'adam', 'component': 'bonus', 'salary': 50},
  {'name': 'adam', 'component': 'base', 'salary': 30000},
]

salary_map = {}
for d in data:
    key = (d['name'], d['component'])
    if key not in salary_map:
        salary_map[key] = d['salary']
    else:
        salary_map[key] += d['salary']

for (name, component), salary in salary_map.items():
    print(name, component, salary)

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