Read from stdin in Python for Common Algorithm Challenges
There are many sites dedicated to host algorithm challenges (e.g UVa Online Judge, Top Coder, Sphere online judge (spoj)). I love spoj because they offer various languages for solution submission. Previously, I learned algorithm in UVa online judge using C++ (i.e. the most popular one in UVa beside Java). Common problem encourage us to read from stdin and there two common patterns:
- Read each line as a test case
- Read first line as N and N test cases follow.
For the first pattern, a typical problem might be looked like:
# Input. Read each line as x, y and print the sum
3 2
7 8
10 15
# Expected output
5
15
25
And you can solve the problem in C++ using the following:
#include <cstdio>
int main() {
int x, y;
while (scanf("%d", &x) != EOF) {
scanf("%d", &y);
printf("%d\n", x + y);
}
}
So how we can do the above in Python? Well, fortunately we
can use sys.stdin like below:
import sys
def main():
for line in sys.stdin:
x, y = line.split(' ')
print int(x) + int(y)
if __name__ == '__main__':
main()
I'm not sure whether this approach is the Pythonic-way. But worked for me pretty well. Let me know in case if you have a better approach.
For the last problem pattern, below is a typical one:
# Input. Read first line as N, N lines follow
# for each test case. For example we still
# asked to sum two ints on each test case.
3
3 2
7 8
10 15
# Expected outupt
5
15
25
It's possible to use previous approach and checking the singular value per line. Or, you can read the first line, which is N, once and loop until N.
import sys
def main():
n = int(sys.stdin.readline())
for i in range(n):
x, y = sys.stdin.readline().strip().split(' ')
print int(x) + int(y)
if __name__ == '__main__':
main()
Hope it helps!