Uses multithreading to guess a "self-describing-number" (which is 6210001000). To build use "g++ -O3 -march=native -std=c++11 -l stdc++ -pthread findSelfDescribingNumber.cpp"

findSelfDescribingNumber.cpp

#include <stdio.h>
#include <thread>
#include <time.h>

void checkNumbers(int offset, int threadCount);
bool checkNumber(const int numbers[10]);
bool checkDigit(const int digit, const int numbers[10]);

int main(int argc, char** argv) {
	int threadCount;
	if (argc > 1) {
		threadCount = std::stoi(argv[1]);
	} else {
		threadCount = 1;
	}
	timespec beginTime, endTime;
	clock_t beginCPUTime, endCPUTime;
	clock_gettime(CLOCK_MONOTONIC, &beginTime);
	beginCPUTime = clock();

	std::thread threads[threadCount];

	for (int i = 0; i < threadCount; i++) {
		threads[i] = std::thread(checkNumbers, i, threadCount);
	}
	for (int i = 0; i < threadCount; i++) {
		threads[i].join();
	}

	clock_gettime(CLOCK_MONOTONIC, &endTime);
	endCPUTime = clock();
	printf("Real time: %f seconds, ", (double) (endTime.tv_sec - beginTime.tv_sec) + (endTime.tv_nsec - beginTime.tv_nsec) / 1e9);
	printf("this equals %f tries per second.\n", ((double) 1e19) / ((endTime.tv_nsec - beginTime.tv_nsec) + 1e9 * (endTime.tv_sec - beginTime.tv_sec)));
	printf("CPU time: %f seconds, ", (double) (endCPUTime - beginCPUTime) / CLOCKS_PER_SEC);
	printf("this equals %f tries per second per CPU.\n", (double) CLOCKS_PER_SEC / (endCPUTime - beginCPUTime) * 1e10);
	return 0;
}

void checkNumbers(int offset, int threadCount) {
	int numbers[10] = {0};
	for (numbers[0] = offset; numbers[0] < 10; numbers[0] += threadCount) {
		for (numbers[1] = 0; numbers[1] < 10; numbers[1]++) {
			for (numbers[2] = 0; numbers[2] < 10; numbers[2]++) {
				for (numbers[3] = 0; numbers[3] < 10; numbers[3]++) {
					for (numbers[4] = 0; numbers[4] < 10; numbers[4]++) {
						for (numbers[5] = 0; numbers[5] < 10; numbers[5]++) {
							for (numbers[6] = 0; numbers[6] < 10; numbers[6]++) {
								for (numbers[7] = 0; numbers[7] < 10; numbers[7]++) {
									for (numbers[8] = 0; numbers[8] < 10; numbers[8]++) {
										for (numbers[9] = 0; numbers[9] < 10; numbers[9]++) {
											if (numbers[0] + numbers[1] + numbers[2] + numbers[3] + numbers[4] + numbers[5] + numbers[6] + numbers[7] + numbers[8] + numbers[9] == 10) {
												if (checkNumber(numbers)) {
													printf("Found one: %d%d%d%d%d%d%d%d%d%d\n", numbers[0], numbers[1], numbers[2], numbers[3], numbers[4], numbers[5], numbers[6], numbers[7], numbers[8], numbers[9]);
												} else if (numbers[0] == 6 && numbers[1] == 2 && numbers[2] == 1 && numbers[3] == 0 && numbers[4] == 0 && numbers[5] == 0 && numbers[6] == 1 && numbers[7] == 0 && numbers[8] == 0 && numbers[9] == 0) {
													printf("He doesn't like me!\n");
												}
											}
										}
									}
								}
							}
						}
					}
				}
			}
		}
	}
}

bool checkNumber(const int numbers[10]) {
	for (int i = 0; i < 10; i++) {
		if (checkDigit(i, numbers)) {
			if (numbers[0] == 6 && numbers[1] == 2 && numbers[2] == 1 && numbers[3] == 0 && numbers[4] == 0 && numbers[5] == 0 && numbers[6] == 1 && numbers[7] == 0 && numbers[8] == 0 && numbers[9] == 0) {
				printf("He doesn't like me at %d!\n", i);
			}
			return false;
		}
	}
	return true;
}

bool checkDigit(const int digit, const int numbers[10]) {
	int counter = 0;
	for (int i = 0; i < 10; i++) {
		if (numbers[i] == digit) {
			counter++;
		}
	}
	return counter != numbers[digit];
}