Hackerrank Python Solutions (Topic wise)

Hackerrank Python solutions done topic wise. Tricky solutions are explained and multiple solutions are mentioned if applicable.

Important Tips Topic-wise

Introduction

• Can also input multiple numbers like this(when numbers entered on new line) : a,b= [int(input()) for _ in range(2)]
• input N and X separated by space(N,X are integers): N,X = map(int,input().split())

Basic Data Types

Strings

Sets

• Update,Union,Intersection,Difference
• add
• remove,discard,pop
• set mutations - A.update(B),A.intersection_update(B)

Math

• Complex numbers-> cmath module

  • Convert a+bj form to complex number z using complex()
  • Convert complex number z to polar coordinates:r and phi
  • r: abs(complex(z))
  • phi: cmath.phase(complex(z))

• It's also possible to calculate pow(a,b,m)

Itertools

• itertools.product - combination of cartesian products.

 print(*(list(itertools.product(A,B)))) # * will print all elements in the list.

• itertools.permutations

Collections

• counter
• Data = namedtuple('Data', columns)
• OrderedDict: An OrderedDict is a dictionary that remembers the order of the keys that were inserted first. If a new entry overwrites an existing entry, the original insertion position is left unchanged.

Date and Time

• calendar.weekday(year, month, day)
• datetime.strptime(timestamp, format)

Errors and Exceptions

• Exceptions -> Errors detected during execution
• Exception handling with try,catch,else,finally: Try: This block will test the excepted error to occur Except: Here you can handle the error Else: If there is no exception then this block will be executed Finally: Finally block always gets executed either exception is generated or not
• import re(regex library)

Classes

Built Ins

• eval keyword usage
• zip function
• EOF Error
• sorted(s, key=lambda x: (x.isdigit(), x.isdigit() and int(x) % 2 == 0, x.isupper(), x))

Functionals

• map
• reduce
• re.match for emails

XML

Closures and Decorators

Numpy

• numpy arrays like lists except only same datatype
• import numpy(can also do import numpy as np)
• arr = numpy.arrays([1,2,3,4],int)
• shape,reshape
• numpy.transpose([[1,2,3],[4,5,6]]),arr.flatten()
• identity

import numpy
print numpy.identity(3) #3 is for  dimension 3 X 3

#Output
[[ 1.  0.  0.]
 [ 0.  1.  0.]
 [ 0.  0.  1.]]

• eye: 2-D array with 1's as the diagonal and 0's elsewhere. The diagonal can be main, upper or lower depending on the optional parameter l .

print(numpy.eye(N,M,k=0)) #k=0 means main diagonal(default value),N is number of rows, M number of cols.

• math operations
• floor,ceil,rint

Debugging