Template for competitive programming

competition.cpp

#include <bits/stdc++.h>

using namespace std;

#define ALL(X) begin(X), end(X)

int main() {
    // solution comes here
}

Input and output is sometimes a bottleneck in the program. The following lines at the beginning of the code make input and output more efficient:

ios::sync_with_stdio(0);
cin.tie(0);

Note that the newline "\n" works faster than endl, because endl always causes a flush operation.

Sometimes the program should read a whole line from the input, possibly containing spaces. This can be accomplished by using the getline function:

 string s;
getline(cin, s);

If the amount of data is unknown, the following loop is useful:

while (cin >> x) {
    // code
}

In some contest systems, files are used for input and output. An easy solution for this is to write the code as usual using standard streams, but add the following lines to the beginning of the code:

freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);