A - Poisonous Oyster
Source: atcoder
Difficulty: 100

Problem Statement
There are four types of oysters, labeled
1
,
2
,
3
, and
4
. Exactly one of these types causes stomach trouble if eaten. The other types do not cause stomach trouble when eaten.
Takahashi ate oysters
1
and
2
, and Aoki ate oysters
1
and
3
. The information on whether each person got sick is given as two strings
S_1
and
S_2
. Specifically,
S_1 =
sick
means Takahashi got sick, and
S_1 =
fine
means Takahashi did not get sick. Likewise,
S_2 =
sick
means Aoki got sick, and
S_2 =
fine
means Aoki did not get sick.
Based on the given information, find which type of oyster causes stomach trouble.
Constraints
Each of
S_1
and
S_2
is
sick
or
fine
.
Input
The input is given from Standard Input in the following format:
S_1
S_2
Output
Print the label of the oyster that causes stomach trouble if eaten.
Sample Input 1
sick fine
Sample Output 1
2
Takahashi (who ate oysters
1
and
2
) got sick, and Aoki (who ate oysters
1
and
3
) did not get sick, so it can be concluded that oyster
2
causes stomach trouble.
Sample Input 2
fine fine
Sample Output 2
4
Neither Takahashi (who ate oysters
1
and
2
) nor Aoki (who ate oysters
1
and
3
) got sick, so it can be concluded that oyster
4
causes stomach trouble.

C++ solution:
#include <bits/stdc++.h>
    using namespace std;
     
    int main() {
      string s1, s2;
      cin >> s1 >> s2;
      if(s1 == s2){
        if(s1 == "sick"){
          cout << 1 << endl;
        }
        else{
          cout << 4 << endl;
        }
      }
      else{
        if(s1 == "sick"){
          cout << 2 << endl;
        }
        else{
          cout << 3 << endl;
        }
      }
    }

Go solution:
package main

import (
	"bufio"
	"fmt"
	"os"
	"strings"
)

func main() {
	sc := bufio.NewScanner(os.Stdin)

	sc.Scan()
	a := strings.Split(sc.Text(), " ")

	S1, S2 := a[0], a[1]

	if S1 == S2 {
		if S1 == "sick" {
			fmt.Println(1)
		} else {
			fmt.Println(4)
		}
	} else {
		if S1 == "sick" {
			fmt.Println(2)
		} else {
			fmt.Println(3)
		}
	}
}

Java solution:
import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.*;
import java.util.function.IntUnaryOperator;
import java.util.function.LongUnaryOperator;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class Main {
    static In in = new In();
    static Out out = new Out(false, false);
    static final long inf = 0x1fffffffffffffffL;
    static final int iinf = 0x3fffffff;
    static final double eps = 1e-9;
    static long mod = 998244353;
    void solve() {
        boolean s1 = in.next().equals("sick");
        boolean s2 = in.next().equals("sick");
        int ans = 0;
        ans += s1 ? 1 : 0;
        ans <<= 1;
        ans += s2 ? 1 : 0;
        out.println(4-ans);
    }

    public static void main(String... args) {
        new Main().solve();
        out.flush();
    }
}

class In {
    private final BufferedInputStream reader = new BufferedInputStream(System.in);
    private final byte[] buffer = new byte[0x10000];
    private int i = 0;
    private int length = 0;

    public int read() {
        if (i == length) {
            i = 0;
            try {
                length = reader.read(buffer);
            } catch (IOException ignored) {
            }
            if (length == -1) {
                return 0;
            }
        }
        if (length <= i) {
            throw new RuntimeException();
        }
        return buffer[i++];
    }

    public String next() {
        StringBuilder builder = new StringBuilder();
        int b = read();
        while (b < '!' || '~' < b) {
            b = read();
        }
        while ('!' <= b && b <= '~') {
            builder.appendCodePoint(b);
            b = read();
        }
        return builder.toString();
    }

    public String nextLine() {
        StringBuilder builder = new StringBuilder();
        int b = read();
        while (b != 0 && b != '\r' && b != '\n') {
            builder.appendCodePoint(b);
            b = read();
        }
        if (b == '\r') {
            read();
        }
        return builder.toString();
    }

    public int nextInt() {
        long val = nextLong();
        if (val < Integer.MIN_VALUE || Integer.MAX_VALUE < val) {
            throw new NumberFormatException();
        }
        return (int)val;
    }

    public long nextLong() {
        int b = read();
        while (b < '!' || '~' < b) {
            b = read();
        }
        boolean neg = false;
        if (b == '-') {
            neg = true;
            b = read();
        }
        long n = 0;
        int c = 0;
        while ('0' <= b && b <= '9') {
            n = n * 10 + b - '0';
            b = read();
            c++;
        }
        if (c == 0 || c >= 2 && n == 0) {
            throw new NumberFormatException();
        }
        return neg ? -n : n;
    }

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

    public char[] nextCharArray() {
        return next().toCharArray();
    }

    public String[] nextStringArray(int n) {
        String[] s = new String[n];
        for (int i = 0; i < n; i++) {
            s[i] = next();
        }
        return s;
    }

    public char[][] nextCharMatrix(int n, int m) {
        char[][] a = new char[n][m];
        for (int i = 0; i < n; i++) {
            a[i] = next().toCharArray();
        }
        return a;
    }

    public int[] nextIntArray(int n) {
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = nextInt();
        }
        return a;
    }

    public int[] nextIntArray(int n, IntUnaryOperator op) {
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = op.applyAsInt(nextInt());
        }
        return a;
    }

    public int[][] nextIntMatrix(int h, int w) {
        int[][] a = new int[h][w];
        for (int i = 0; i < h; i++) {
            a[i] = nextIntArray(w);
        }
        return a;
    }

    public long[] nextLongArray(int n) {
        long[] a = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = nextLong();
        }
        return a;
    }

    public long[] nextLongArray(int n, LongUnaryOperator op) {
        long[] a = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = op.applyAsLong(nextLong());
        }
        return a;
    }

    public long[][] nextLongMatrix(int h, int w) {
        long[][] a = new long[h][w];
        for (int i = 0; i < h; i++) {
            a[i] = nextLongArray(w);
        }
        return a;
    }

    public List<List<Integer>> nextGraph(int n, int m, boolean directed) {
        List<List<Integer>> res = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            res.add(new ArrayList<>());
        }
        for (int i = 0; i < m; i++) {
            int u = nextInt() - 1;
            int v = nextInt() - 1;
            res.get(u).add(v);
            if (!directed) {
                res.get(v).add(u);
            }
        }
        return res;
    }
}

class Out {
    private final PrintWriter out = new PrintWriter(System.out);
    private final PrintWriter err = new PrintWriter(System.err);
    public boolean autoFlush;
    public boolean enableDebug;

    public Out(boolean autoFlush, boolean enableDebug) {
        this.autoFlush = autoFlush;
        this.enableDebug = enableDebug;
    }

    public void debug(Object... args) {
        if (!enableDebug) {
            return;
        }
        if (args == null || args.getClass() != Object[].class) {
            args = new Object[] {args};
        }
        err.println(Arrays.stream(args).map(obj -> format(obj, true)).collect(Collectors.joining(" ")));
        err.flush();
    }

    private String format(Object obj, boolean canMultiline) {
        if (obj == null) return "null";
        Class<?> clazz = obj.getClass();
        if (clazz == Double.class) return String.format("%.10f", obj);
        if (clazz == int[].class) return Arrays.toString((int[])obj);
        if (clazz == long[].class) return Arrays.toString((long[])obj);
        if (clazz == char[].class) return String.valueOf((char[])obj);
        if (clazz == boolean[].class) return IntStream.range(0, ((boolean[])obj).length).mapToObj(i -> ((boolean[])obj)[i] ? "1" : "0").collect(Collectors.joining());
        if (clazz == double[].class) return Arrays.toString(Arrays.stream((double[])obj).mapToObj(a -> format(a, false)).toArray());
        if (canMultiline && clazz.isArray() && clazz.componentType().isArray()) return Arrays.stream((Object[])obj).map(a -> format(a, false)).collect(Collectors.joining("\n"));
        if (clazz == Object[].class) return Arrays.toString(Arrays.stream((Object[])obj).map(a -> format(a, false)).toArray());
        if (clazz.isArray()) return Arrays.toString((Object[])obj);
        return String.valueOf(obj);
    }

    public void println(Object... args) {
        if (args == null || args.getClass() != Object[].class) {
            args = new Object[] {args};
        }
        out.println(Arrays.stream(args)
                .map(obj -> obj instanceof Double ? String.format("%.10f", obj) : String.valueOf(obj))
                .collect(Collectors.joining(" ")));
        if (autoFlush) {
            out.flush();
        }
    }

    public void println(char a) {
        out.println(a);
        if (autoFlush) {
            out.flush();
        }
    }

    public void println(int a) {
        out.println(a);
        if (autoFlush) {
            out.flush();
        }
    }

    public void println(long a) {
        out.println(a);
        if (autoFlush) {
            out.flush();
        }
    }

    public void println(double a) {
        out.println(String.format("%.10f", a));
        if (autoFlush) {
            out.flush();
        }
    }

    public void println(String s) {
        out.println(s);
        if (autoFlush) {
            out.flush();
        }
    }

    public void println(char[] s) {
        out.println(String.valueOf(s));
        if (autoFlush) {
            out.flush();
        }
    }

    public void println(int[] a) {
        StringJoiner joiner = new StringJoiner(" ");
        for (int i : a) {
            joiner.add(Integer.toString(i));
        }
        out.println(joiner);
        if (autoFlush) {
            out.flush();
        }
    }

    public void println(long[] a) {
        StringJoiner joiner = new StringJoiner(" ");
        for (long i : a) {
            joiner.add(Long.toString(i));
        }
        out.println(joiner);
        if (autoFlush) {
            out.flush();
        }
    }

    public void flush() {
        err.flush();
        out.flush();
    }
}

JavaScript solution:
const main = function(input) {
    const [S1, S2] = input[0].split(" ").map((a) => a == "sick");
    if (S1 && S2) {
        console.log(1)
    } else if (S1 && !S2) {
        console.log(2)
    } else if (!S1 && S2) {
        console.log(3)
    } else {
        console.log(4)
    }
}
main(require("fs").readFileSync("/dev/stdin", "utf8").split("\n"));

Python solution:
def identify_bad_oyster(S1, S2):
    if S1 == "sick" and S2 == "fine":
        return 2
    elif S1 == "fine" and S2 == "sick":
        return 3
    elif S1 == "sick" and S2 == "sick":
        return 1
    elif S1 == "fine" and S2 == "fine":
        return 4

# 入力を受け取る
S1, S2 = input().split()

# 関数を使って結果を表示
print(identify_bad_oyster(S1, S2))

Ruby solution:
s = gets.split(' ')

if s[0] == 'sick' && s[1] == 'sick'
  puts 1
elsif s[0] == 'sick' && s[1] == 'fine'
  puts 2
elsif s[0] == 'fine' && s[1] == 'sick'
  puts 3
else
  puts 4
end