The input / output part of tips you should know when programming in Python2 has been split.
The input / output method for competitive programming in Python is illustrated. Input / output codes are often a hurdle when learning a language for the first time, but once you remember it, it's a pattern, so you want to remember it quickly.
The Python version is ** 2.7.5 ** (Python3 has very different specifications such as input / output, so it is recommended to refer to other articles).
Receiving standard input 1-Qiita
input
S
S is a character string.
S = raw_input()
input
N
N is an integer or floating point number.
N = input()
input
A B C
A, B, and C are all character strings.
l = raw_input().split()
print l[0] #The value of A is output
print l[1] #The value of B is output
print l[2] #The value of C is output
split () splits the string into a list separated by spaces.
input
A B C
A, B, and C are all integers or floating point numbers.
If A, B, and C are all integers,
l = map(int, raw_input().split())
print l[0] # A
print l[1] # B
print l[2] # C
In short, the input received in the string type is divided by spaces and assigned to the list, and each element is mapped to the integer type.
The number of elements may be given to the input data, but in the case of Python it does not matter much even if it is not used.
For floating point numbers
l = map(float, raw_input().split())
Note that if you use ʻint` for floating point numbers, the value will be truncated.
A, B, C = map(int, raw_input().split())
print A # A
print B # B
print C # C
If the number of elements in the list matches the number on the left side, each element of the list can be assigned to each variable on the left side. It seems that this type of assignment is called "unpacked assignment".
In the case of competitive programming, it should be used only when the number of input elements is clear and small.
Although it is rarely seen, if a character string or an integer is mixed in one line, one line is received as a character string for the time being, and later converted using ʻint () , float () `, etc.
input
N
a1
a2
a3
...
aN
a1, a2, ..., aN are N integers.
N = input()
a = []
for i in range(N):
a.append(input())
print a # [a1, a2, a3, ..., aN]
It's OK.
@ zakuro9715 taught me.
This code can also be expressed as follows using list comprehension notation. N-line input can be written in one line and is beautiful.
N = input()
a = [input() for i in range(N)]
print a # [a1, a2, a3, ..., aN]
Aizu Online Judge (AOJ) A format often seen.
input
a1
a2
a3
...
-1
a1, a2, ..., are all integers. -1 represents the end of input.
a = []
while True:
n = input()
if n == -1:
break
a.append(n)
print a # [a1, a2, a3, ..., aN]
I also see this occasionally on AOJ. It's hard to debug, and I personally hate it.
input
a1
a2
a3
...
(EOF)
a1, a2, ..., are all integers. Read until EOF comes.
import sys
a = []
for line in sys.stdin:
a.append(int(line))
print a # [a1, a2, a3, ...]
A summary feeling so far.
input
N M
a11 a12 a13 ... a1M
a21 a22 a23 ... a2M
a31 a32 a33 ... a3M
...
aN1 aN2 aN3 ... aNM
a11, a12, ..., aNM are integers.
N, M = map(int, raw_input().split())
a = []
for i in range(M):
a.append(map(int, raw_input().split()))
print a
# [[a11, a12, a13, ..., a1M]
# [a21, a22, a23, ..., a2M]
# ...
# [aN1, aN2, aN3, ..., aNM]]
Maybe it's okay if you keep this down.
I learned from @ t2y.
By using a generator, it is possible to receive input over multiple lines well.
For example
input
a1
a2
a3
...
(EOF)
a1, a2, ..., are all character strings. Read until EOF comes.
If the format is like
def get_input():
while True:
try:
yield ''.join(raw_input())
except EOFError:
break
if __name__ == '__main__':
a = list(get_input()) # [a1, a2, a3, ...]
To do.
Besides, the contents of get_input (),
def get_input():
while True:
try:
s = raw_input()
if s == '-1':
break
yield ''.join(s)
except EOFError:
break
By changing to, it is possible to receive a slightly complicated input such as "read" -1 "or until the end of input".
output
A
Includes a line break at the end.
print A
Both integer type and character string type can be output. In addition, debugging of lists and dictionaries can be done as it is with the print statement.
To be honest, I haven't seen it, but for the time being, for studying.
output
A
Does not include line breaks at the end.
import sys
sys.stdout.write(A)
I often see this.
output
A B C
Includes a line break at the end.
print A, B, C
In the print statement, if you put , after the variable, the line break will be converted to a half-width space.
Python Tips: I want to output a character string without line breaks --Life with Python
output
A,B,C
A, B, and C are all character strings. Includes a line break at the end.
print ','.join([A, B, C])
join () corresponds to the inverse operation of split () and returns the concatenation of each element of the argument string list with the receiver string.
Note that all elements of the list must be of type string.
Here, for example, if A, B, and C are integers,
print ','.join(map(str, [A, B, C]))
Like, after converting each element to a character string by str (), join.
There are cases where you want to output in a free format, such as the printf function in C ++.
output
Case 1: A B
Both A and B are integers. Includes a line break at the end.
print 'Case 1: {0} {1}'.format(A, B)
format () takes a variadic argument and returns a string containing the value of the i-th argument in'{i}'.
You can do most of the things you can do with printf, such as radix conversion and digit alignment at the time of output, with format ().
For details, see Reference.