Problem 52: Permuted Multiples

Problem 52 source code

C++

#include <algorithm>
#include <iostream>
#include <string>

namespace {

struct Options {
    int max_multiplier = 6;
    bool run_checkpoints = true;
};

bool parse_int_after_prefix(const std::string& arg, const std::string& prefix, int& value) {
    if (arg.rfind(prefix, 0U) != 0U) {
        return false;
    }
    const std::string tail = arg.substr(prefix.size());
    if (tail.empty()) {
        return false;
    }

    int parsed = 0;
    for (char c : tail) {
        if (c < '0' || c > '9') {
            return false;
        }
        parsed = parsed * 10 + static_cast<int>(c - '0');
    }
    value = parsed;
    return true;
}

bool parse_arguments(int argc, char** argv, Options& options) {
    for (int i = 1; i < argc; ++i) {
        const std::string arg(argv[i]);
        if (arg == "--skip-checkpoints") {
            options.run_checkpoints = false;
            continue;
        }
        if (parse_int_after_prefix(arg, "--max-multiplier=", options.max_multiplier)) {
            continue;
        }

        std::cerr << "Unknown argument: " << arg << '\n';
        return false;
    }
    return options.max_multiplier >= 2;
}

std::string sorted_digits(int value) {
    std::string s = std::to_string(value);
    std::sort(s.begin(), s.end());
    return s;
}

int solve(const int max_multiplier) {
    for (int x = 1;; ++x) {
        const std::string signature = sorted_digits(x);
        bool ok = true;
        for (int k = 2; k <= max_multiplier; ++k) {
            if (sorted_digits(k * x) != signature) {
                ok = false;
                break;
            }
        }
        if (ok) {
            return x;
        }
    }
}

bool run_checkpoints() {
    if (sorted_digits(125874) != sorted_digits(251748)) {
        std::cerr << "Checkpoint failed for 125874" << '\n';
        return false;
    }
    return true;
}

}  // namespace

int main(int argc, char** argv) {
    Options options;
    if (!parse_arguments(argc, argv, options)) {
        return 1;
    }
    if (options.run_checkpoints && !run_checkpoints()) {
        return 2;
    }

    std::cout << solve(options.max_multiplier) << '\n';
    return 0;
}

Python

import sys

def sorted_digits(value):
    return ''.join(sorted(str(value)))

def solve(max_multiplier):
    x = 1
    while True:
        signature = sorted_digits(x)
        ok = True
        for k in range(2, max_multiplier + 1):
            if sorted_digits(k * x) != signature:
                ok = False
                break
        if ok:
            return x
        x += 1

def run_checkpoints():
    if sorted_digits(125874) != sorted_digits(251748):
        sys.stderr.write("Checkpoint failed for 125874\n")
        return False
    return True

def parse_arguments(args):
    max_multiplier = 6
    run_checkpoints_flag = True
    
    i = 1
    while i < len(args):
        arg = args[i]
        if arg == "--skip-checkpoints":
            run_checkpoints_flag = False
            i += 1
            continue
        
        if arg.startswith("--max-multiplier="):
            try:
                value_str = arg[len("--max-multiplier="):]
                if not value_str:
                    return None, False
                max_multiplier = int(value_str)
                i += 1
                continue
            except ValueError:
                return None, False
        
        sys.stderr.write(f"Unknown argument: {arg}\n")
        return None, False
    
    if max_multiplier < 2:
        return None, False
    
    return {"max_multiplier": max_multiplier, "run_checkpoints": run_checkpoints_flag}, True

def main():
    args = sys.argv[1:]
    
    options, success = parse_arguments(args)
    if not success:
        sys.exit(1)
    
    if options["run_checkpoints"] and not run_checkpoints():
        sys.exit(2)
    
    result = solve(options["max_multiplier"])
    print(result)

if __name__ == "__main__":
    main()

Java

import java.util.*;

class Euler52 {

    private static class Options {
        int maxMultiplier = 6;
        boolean runCheckpoints = true;
    }

    private static boolean parseIntAfterPrefix(String arg, String prefix, Options options) {
        if (!arg.startsWith(prefix)) {
            return false;
        }
        String tail = arg.substring(prefix.length());
        if (tail.isEmpty()) {
            return false;
        }

        int parsed = 0;
        for (int i = 0; i < tail.length(); i++) {
            char c = tail.charAt(i);
            if (c < '0' || c > '9') {
                return false;
            }
            parsed = parsed * 10 + (c - '0');
        }
        options.maxMultiplier = parsed;
        return true;
    }

    private static boolean parseArguments(String[] args, Options options) {
        for (String arg : args) {
            if ("--skip-checkpoints".equals(arg)) {
                options.runCheckpoints = false;
                continue;
            }
            if (parseIntAfterPrefix(arg, "--max-multiplier=", options)) {
                continue;
            }

            System.err.println("Unknown argument: " + arg);
            return false;
        }
        return options.maxMultiplier >= 2;
    }

    private static String sortedDigits(int value) {
        char[] chars = Integer.toString(value).toCharArray();
        Arrays.sort(chars);
        return new String(chars);
    }

    private static int solve(int maxMultiplier) {
        for (int x = 1; ; ++x) {
            String signature = sortedDigits(x);
            boolean ok = true;
            for (int k = 2; k <= maxMultiplier; ++k) {
                if (!sortedDigits(k * x).equals(signature)) {
                    ok = false;
                    break;
                }
            }
            if (ok) {
                return x;
            }
        }
    }

    private static boolean runCheckpoints() {
        if (!sortedDigits(125874).equals(sortedDigits(251748))) {
            System.err.println("Checkpoint failed for 125874");
            return false;
        }
        return true;
    }

    public static void main(String[] args) {
        Options options = new Options();
        if (!parseArguments(args, options)) {
            System.exit(1);
        }
        if (options.runCheckpoints && !runCheckpoints()) {
            System.exit(2);
        }

        System.out.println(solve(options.maxMultiplier));
    }
}