usaco-guide/content/1_Intro/Example_Problem.md

id	title	author	problems	prerequisites	description
ex-prob	An Example Problem	Nathan Wang, Benjamin Qi, Darren Yao	bronze_promote bronze_word bronze_paint bronze_square	Intro - Data Types Intro - Input & Output	Solutions for an "USACO Bronze - Fence Painting" in multiple languages.

Technical Specifications for USACO Contests

Example: Fence Painting

USACO will automatically add a newline to the end of your file if it does not end with one. Make sure not to output trailing spaces!

C++

Here is some info about <bits/stdc++.h\> if you are not familiar with it.

Method 1

Use freopen. If you comment out both of the lines containing freopen then the program reads from standard in and writes to standard out as usual.

#include <bits/stdc++.h>
using namespace std;

int main() {
	freopen("paint.in","r",stdin); // reuse standard in to read from "paint.in"
	freopen("paint.out","w",stdout); // reuse standard out to write to "paint.out"
	vector<bool> cover(100);
	int a, b, c, d; cin >> a >> b >> c >> d;
	for (int i = a; i < b; ++i) cover[i] = 1;
	for (int i = c; i < d; ++i) cover[i] = 1;
	int ans = 0; 
	for (int i = 0; i < 100; ++i) ans += cover[i];
	cout << ans;
	// cout << ans << endl; is OK
	// cout << ans << "\n"; is OK
	// cout << ans << " "; is NOT OK
	// cout << ans << "\n\n"; is NOT OK
}

Also, including ios_base::sync_with_stdio(0); cin.tie(0); in the main function can speed up input & output significantly on some tasks. See here and StackOverflow for more information.

• Actually, the former link says that it is supposedly prohibited to use freopen to redirect cin and cout if ios_base::sync_with_stdio(0); cin.tie(0); is included, but it works properly as far as I know.

Method 2

Use ifstream & ofstream.

#include <bits/stdc++.h>
using namespace std;

int main() {
	ifstream fin("paint.in");
	ofstream fout("paint.out");
	vector<bool> cover(100);
	int a, b, c, d; fin >> a >> b >> c >> d;
	for (int i = a; i < b; ++i) cover[i] = 1;
	for (int i = c; i < d; ++i) cover[i] = 1;
	int ans = 0; 
	for (int i = 0; i < 100; ++i) ans += cover[i];
	fout << ans;
}

Java

import java.io.*;
import java.util.*;
public class paintSol { // must be declared in paintSol.java
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new FileReader("paint.in"));
		PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter("paint.out")));
		int[] cover = new int[100];

		StringTokenizer st = new StringTokenizer(br.readLine());
		int a = Integer.parseInt(st.nextToken()), b = Integer.parseInt(st.nextToken());
		st = new StringTokenizer(br.readLine());
		int c = Integer.parseInt(st.nextToken()), d = Integer.parseInt(st.nextToken());

		for (int i = a; i < b; i++) cover[i] = 1;
		for (int i = c; i < d; i++) cover[i] = 1;
		int ans = 0; 
		for (int i = 0; i < 100; i++) ans += cover[i];
		pw.println(ans); 
		pw.close(); // make sure to include this line -- flushes the output.
	}
}

Alternatively, we can use the InputReader given in the previous module.

import java.util.*;
import java.io.*;

public class template {

    static class InputReader {
        BufferedReader reader;
        StringTokenizer tokenizer;

        public InputReader() throws FileNotFoundException {
            reader = new BufferedReader(new FileReader("paint.in"));
            tokenizer = null;
        }

        String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public double nextDouble() {
            return Double.parseDouble(next());
        }
    }

    public static void main(String[] args) throws FileNotFoundException, IOException {

		InputReader r = new InputReader();
		PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter("paint.out")));

		int[] cover = new int[100];
		for (int i = a; i < b; i++) cover[i] = 1;
		for (int i = c; i < d; i++) cover[i] = 1;
		int ans = 0; 
		for (int i = 0; i < 100; i++) ans += cover[i];
		
		pw.println(ans); 
		pw.close(); // flush output
    }
}

Python 3

See here for documentation about file I/O.

fin = open("paint.in","r")
fout = open("paint.out","w")
cover = [0 for i in range(100)]
a,b = map(int,fin.readline().split())
c,d = map(int,fin.readline().split())
for i in range(a,b):
	cover[i] = 1
for i in range(c,d):
	cover[i] = 1
ans = 0
for i in range(100):
	ans += cover[i]
fout.write(str(ans))

Introductory Problems

The following require relatively little programming experience and no algorithmic knowledge. Do as many as you want, then move on! You do not have to do all of them.

• Promotion Counting
• Word Processor
• Square Pasture