Python - Competitive Programming Tricks

__python_tricks__

Python - Competitive Programming Tricks

collection.py

# Initialising a list filled with value
arr = [0]*10
print(arr)

x = 1
arr = [x] * 10
print(arr)

# Reverse
arr = [1, 2, 3, 4, 5]
print(arr, '<>', arr[::-1])
s = 'Hello world!'
print(s, '<>', s[::-1])

# Get dictionary
dictionary = {'a': 1, 'b':2}
print(dictionary['a'])

try:
    print(dictionary['c'])
except Exception as e:
    print('Error:', e)

print(dictionary.get('c', 0)) # Default value is 0

# For Else
arr = []
for x in arr:
    print(x)
else:
    print('Empty array')

# Copy
arr = [1, 2, 3]
print(arr)

arr2 = arr.copy()
arr[0] = 0

print(arr)
print(arr2)

in.py

# Read an integer from standard input:
n = int(input())

# Read an integer array from standard input:
arr = list(map(int, input().split()))

# Change input from standard input to file:
import sys
sys.stdin = open('in.txt', 'r')

operator.py

# Floor div
x = 6 // 4
print(x)

# Elvis
x = 'true' if True else 'false'
print(x)

x = ('false', 'true')[2>1] # (falseValue, trueValue)[bool(<expression>)]
print(x)

# Swap
a = 1
b = 2
print(a, b)
a, b = b, a
print(a, b)

# Chained Comparison
a = 100
print(9>a<1001)
print(9<a<1001)
print(9<=a==100)

out.py

# Print variable to Standard output:
x = 5
print(x)
print(x, end="") # Print without break line

print() # Print break line

s = "Hello world"
print(s)

print(s, x)

arr = [1, 2, 3]
print(arr)
print(*arr)

dictionary = {'x': 1, 'y': 2, 'z': 3}
print(dictionary)
print(*dictionary)

# Change output from standard output to file:
import sys
sys.stdout = open('out.txt', 'w')

strings.py

# String Interpolation
result = 100

s = 'result is {}'.format(result)
print(s)

s = f'result is {result}' # From Python 3.6
print(s)

s = 'result is %s' % (result)
print(s)

# String join
arr = [1, 2, 3]
s = ''.join(map(str, arr)) # Convert list integer to string
print(s)
s = '\n'.join(map(str, arr))
print(s)

# String to array of character
s = 'abcdef'
arr = list(s)
print(arr)

# String split
s = '1 2 3'
arr = list(map(int, s.split())) # Default split parameter is space
print(arr)

The elapsed time during the whole program in seconds

from time import perf_counter
    
# Start the stopwatch / counter
t1_start = perf_counter()

# Your code

# Stop the stopwatch / counter
t1_stop = perf_counter()
 
print("Elapsed time during the whole program in seconds:", t1_stop-t1_start)

unittest_run.py

# To run all tests: python3 unittest_run.py
# To run single test: python3 unittest_run.py {test_function_name}, ex: python3 unittest_run.py testInOut

import sys
import os

if __name__ == '__main__':
    args = " ".join(map(lambda x: f'Test.{x}', sys.argv[1:]))
    cmd = f'python3 -m unittest -v unittest_test.py {args}'
    os.system(cmd)

unittest_solution.py

# This program read two integer from Standard Input and print sum

def compute(a, b):
    return a+b

def main():
    a, b = map(int, input().split())
    result = compute(a, b)
    print(result)

if __name__ == '__main__':
    main()

unittest_test.py

# This program test unittest_solution.py

import sys
sys.dont_write_bytecode = True

import unittest
import unittest_solution as solution

class Test(unittest.TestCase):
    def tearDown(self):
        try:
            import os
            os.remove('in.txt')
            os.remove('out.txt')
            os.remove('result.txt')
        except:
            pass

    # Test direct sample
    def testSample(self):
        self.assertEqual(solution.compute(1, 2), 3)
        self.assertEqual(solution.compute(2, 2), 4)
        self.assertEqual(solution.compute(1, 1), 2)

    # Test input, output
    def testInOut(self):
        with open('in.txt', 'w') as fi:
            print('1 2', file=fi)
        with open('out.txt', 'w') as fo:
            print('3', file=fo)

        sys.stdin = open('in.txt', 'r')
        sys.stdout = open('result.txt', 'w')
        solution.main()

        sys.stdin.close()
        sys.stdout.close()

        import filecmp
        self.assertTrue(filecmp.cmp('result.txt', 'out.txt'))


if __name__ == '__main__':
    unittest.main()

utility.py

# Print 2d array pretty
def printPretty2dArray(arr):
    print('\n'.join(['\t'.join([str(cell) for cell in row]) for row in arr]))

matrix = [[1, 2, 3], [4, 5, 6]]
print(matrix)
printPretty2dArray(matrix)