[Python] Basic knowledge used in AtCoder
AtCoder beginners can solve problems Make a note of the knowledge that may be useful.
input
Receive various inputs.
Receiving letters
S = input()
Receiving numbers
N = int(input())
Receiving blank numbers
A,B = map(int,input().split())
Receive the number of inputs and receive the number of inputs Writing using square brackets is called "inclusive notation"
N = int(input()) #Number of inputs
l = list(int(input()) for _ in range(N)) #Get N numerical inputs as a list
#Or
l = [int(input()) for _ in range(N)] #Get N numerical inputs as a list
Receives the number of inputs and receives blank numbers for that number of times
Q = int(input())
L = [0]*Q
R = [0]*Q
for i in range(Q):
L[i], R[i] = map(int, input().split())
#Or
l = list(list(map(int, input().split())) for _ in range(Q))
l = [list(map(int,(input().split()))) for _ in range(Q)]
If you want to change the string later, take it as a list of characters
Python #input
T = list(input())
T[0] = "p"
print("".join(T))
python
output
Output list with blanks
l = [1,2,3]
print(*l)
1 2 3
Output list without whitespace join
l = [1,2,3]
l = map(str,l) #Since join is for a string, convert it to a string
print("".join(l))
123
format
name = "Suzuki"
height = 170
weight = 60
print("{0}Is tall{1}cm, weight{2}kg".format(name,height,weight))
Mr. Suzuki is 170 cm tall and weighs 60 kg.
Repeating strings, multiplying strings
s = "Python"
print(s*3)
PythonPythonPython
Ternary operator
flag = 1
print("Yes" if flag else "No")
print("Yes" if not flag else "No")
Yes
No
Calculate formula from string eval
print(eval("1+2"))
3
Sum of each digit
Convert a number to a character string and decompose it into numbers of each digit to find the sum
x = 1357
sum(int(i) for i in str(x))
#Or
sum(list(map(int, str(x))))
Absolute value
abs(-2)
Merchandise and remainder
x = 10; y = 3
q = x // y
mod = x % y
q, mod = divmod(x, y)
list
sort Sort in descending order
l = [1,3,5,2,4]
l.sort()
l2 = sorted(l) #Put in another variable
l.sort(reverse = True) #Sort in descending order
l2 = sorted(l, reverse = True) #Sort in descending order and put in another variable
Sort by second element
l = [[1,5],[2,2],[3,4]]
l.sort(key=lambda x:x[1])
print(l)
[[2, 2], [3, 4], [1, 5]]
Slice operation Output list in reverse order
l = [1,2,3,4,5]
print(l[2:]) #Second and subsequent
print(l[:2]) #Up to the second
print(l[2:4]) #From 2nd to 4th
print(l[-2:]) #Two from the back
print(l[::-1]) #Output list in reverse order
print(l[::2]) #Skip one
print(l[1::2]) #Skip one after the second
[3, 4, 5]
[1, 2]
[3, 4]
[4, 5]
[5, 4, 3, 2, 1]
[1, 3, 5]
[2, 4]
enumerate Get list index and element at the same time
l = ["National language","Math","Science","society","English"]
#The second argument is the start index
for i,subject in enumerate(l, 1):
print(str(i)+"The second is"+subject)
The first is the national language
The second is mathematics
The third is science
Fourth is society
5th is english
Greatest common divisor, least common multiple
from fractions import gcd
x = 8
y = 12
gcd(x,y) #Greatest common divisor
(x*y)//gcd(x,y) #Least common multiple
Permutations, combinations
from itertools import permutations, combinations
balls = [1, 2, 3]
print(list(permutations(balls, 3))) #permutation
print(list(combinations(balls, 2))) #combination
[(1, 2, 3), (1, 3, 2), (2, 1, 3), (2, 3, 1), (3, 1, 2), (3, 2, 1)]
[(1, 2), (1, 3), (2, 3)]
ASCII code ord, chr
【ord】 Convert to ASCII code 【chr】 Convert ASCII code to characters
c = input()
print(chr(ord(c) + 1))
Primality test
To determine the prime number, check if there is a number divisible up to $ \ sqrt {n} $.
def is_prime(n):
if n == 1:
return False
for i in range(2,int(n**0.5)+1):
if n % i == 0:
return False
return True
Distance between two points
import numpy as np
a = np.array((1,2))
b = np.array((5,6))
distance = np.linalg.norm(a-b)
Initialization at infinity
f_inf = float('inf')
f_inf_minus = -float('inf')
Remove duplicate values
l = [4,2,1,3,4,3,2]
print(set(l))
{1, 2, 3, 4}
Check the number of occurrences of the alphabet
import string
val_str = "hello everyone"
d = {}
alphas = string.ascii_lowercase
for key in alphas:
d[key] = 0
for key in val_str:
if key in alphas:
d[key] += 1
for i in d:
print("{0} : {1}".format(i,d[i]))
a : 0
b : 0
c : 0
d : 0
e : 4
f : 0
g : 0
h : 1
i : 0
j : 0
k : 0
l : 2
m : 0
n : 1
o : 2
p : 0
q : 0
r : 1
s : 0
t : 0
u : 0
v : 1
w : 0
x : 0
y : 1
z : 0
When examining only what appears
import string
from collections import defaultdict
val_str = "hello everyone"
d = defaultdict(int)
for key in val_str:
d[key] += 1
for i in d:
print("{0} : {1}".format(i,d[i]))
h : 1
e : 4
l : 2
o : 2
: 1
v : 1
r : 1
y : 1
n : 1
2 minutes search
A,B,Z = [int(i) for i in input().split()]
max = 10 ** 9 + 1
min = 0
while max - min > 1:
avr = (max + min) // 2
sum = A * avr + B * len(str(avr))
if sum <= Z:
min = avr
else:
max = avr
print(min)
Output index in order of score
Output using a dictionary (dict)
l = [7,6,13,10,7]
dic = {}
for i,score in enumerate(l):
dic[i+1] = score
dic = sorted(dic.items(), key=lambda x:x[1], reverse = True)
for i in dic:
print("{0}, score:{1}".format(i[0],i[1]))
3, score:13
4, score:10
1, score:7
5, score:7
2, score:6
On the contrary, the ranking is output
l = [7,6,13,10,7]
l2 = sorted(l, reverse = True)
for i in l:
print(l2.index(i) + 1)
3
5
1
2
3
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