Следующий код сохраняет ваш дизайн и должен дать хотя бы решение, если оно существует. Вложенные if
и for
могут быть упрощены в более элегантном решении с использованием рекурсивной функции. С такой рекурсивной функцией вы также можете перечислить все решения.
Вместо того чтобы иметь несколько копий строки, вы можете использовать итератор, который определяет начало поиска. В коде переменная start
- это итератор.
#include <string>
#include <iostream>
#include <sstream>
using namespace std;
bool ExistDigit(const string & currentNumber, int& start, int look1) {
int currentDigit;
int length = currentNumber.length();
for (int i = length - 1 - start; i >= 0; i--) {
currentDigit = currentNumber[i] - '0';
if (currentDigit == look1) {
start = length - i;
return true;
}
}
return false;
}
int main() {
string originalNumber;//hold number. Must be string because number can be too long for ints
cin >> originalNumber;
stringstream answer;
answer << "YES";
//look for 0's and 8's. they are solutions by their own
int start = 0;
if (ExistDigit(originalNumber, start, 0)) {
answer << "\n0";
}
else {
start = 0;
if (ExistDigit(originalNumber, start, 8)) {
answer << "\n8";
}
else {
start = 0;
//look for 'even'32, 'even'72, 'odd'12, 'odd'52, 'odd'92
//these are the possibilities for multiples of 8 ended with 2
if (ExistDigit(originalNumber, start, 2)) {
for (int look2 = 1; look2 < 10; look2 += 4) {
int startAttempt1 = start;
if (ExistDigit(originalNumber, startAttempt1, look2)) { // 'odd'
for (int look3 = 1; look3 < 10; look3 += 2) {
int startAttempt2 = startAttempt1;
if (ExistDigit(originalNumber, startAttempt2, look3))
answer << "\n" << look3 << look2 << "2";
};
}
};
for (int look2 = 3; look2 < 10; look2 += 4) {
int startAttempt1 = start;
if (ExistDigit(originalNumber, startAttempt1, look2)) // 'even'
answer << "\n" << look2 << "2";
};
}
//look for 'odd'36, 'odd'76, 'even'12, 'even'52, 'even'92
//these are the possibilities for multiples of 8 ended with 2
else if (ExistDigit(originalNumber, start, 6)) {
for (int look2 = 3; look2 < 10; look2 += 4) {
int startAttempt1 = start;
if (ExistDigit(originalNumber, startAttempt1, look2)) { // 'odd'
for (int look3 = 1; look3 < 10; look3 += 2) {
int startAttempt2 = startAttempt1;
if (ExistDigit(originalNumber, startAttempt2, look3))
answer << "\n" << look3 << look2 << "6";
};
}
};
for (int look2 = 1; look2 < 10; look2 += 4) {
int startAttempt1 = start;
if (ExistDigit(originalNumber, startAttempt1, look2)) // 'even'
answer << "\n" << look2 << "6";
};
}
//look for 'even'24, 'even'64, 'odd'44, 'odd'84, 'odd'04
//these are the possibilities for multiples of 8 ended with 2
else if (ExistDigit(originalNumber, start, 6)) {
for (int look2 = 0; look2 < 10; look2 += 4) {
int startAttempt1 = start;
if (ExistDigit(originalNumber, startAttempt1, look2)) { // 'odd'
for (int look3 = 1; look3 < 10; look3 += 2) {
int startAttempt2 = startAttempt1;
if (ExistDigit(originalNumber, startAttempt2, look3))
answer << "\n" << look3 << look2 << "4";
};
}
};
for (int look2 = 2; look2 < 10; look2 += 4) {
int startAttempt1 = start;
if (ExistDigit(originalNumber, startAttempt1, look2)) // 'even'
answer << "\n" << look2 << "4";
};
}
}
}
cout << answer.str() << std::endl;
return 0;
}
Это решение, когда вы ищете подслово, состоящее из последовательных символов в десятичной текстовой форме.
#include <string>
#include <iostream>
bool ExistDigit(const std::string& number, int look) { // look1 = 2**look
// look for a subword of size look that is divisible by 2**look = 1UL << look
for (int i = (int) number.size()-1; i >= 0; --i) {
bool hasFound = false;
unsigned long val = 0;
int shift = look-1;
if (i-shift <= 0)
shift = i;
for (; shift >= 0; --shift) {
val *= 10;
val += (number[i-shift] - '0');
};
if (val % (1UL << look) == 0)
return true;
};
return false;
}
int main(int argc, char** argv) {
std::string val;
std::cin >> val;
if (ExistsDigit(val, 3) /* since 8 = 2**3 = (1 << 3) */)
std::cout << "have found a decimal subword divisible by 8" << std::endl;
else
std::cout << "have not found any decimal subword divisible by 8" << std::endl;
return 0;
}
Если вы, вероятно, найти подслово последовательных битов в двоичном виде числа, вам нужно преобразовать число в большом целое число, а затем сделать подобный поиск.
Это (минимальное тестирование) решение без какого-либо вызова внешней библиотеки, такой как gmp, для преобразования текста в большое целое число. Это решение использует побитовые операции (<<
, &
).
#include <iostream>
#include <string>
#include <vector>
int
ExistDigit(const std::string & currentNumber, int look) { // look1 = 2^look
std::vector<unsigned> bigNumber;
int length = currentNumber.size();
for (int i = 0; i < length; ++i) {
unsigned carry = currentNumber[i] - '0';
// bigNumber = bigNumber * 10 + carry;
for (int index = 0; index < bigNumber.size(); ++index) {
unsigned lowPart = bigNumber[index] & ~(~0U << (sizeof(unsigned)*4));
unsigned highPart = bigNumber[index] >> (sizeof(unsigned)*4);
lowPart *= 10;
lowPart += carry;
carry = lowPart >> (sizeof(unsigned)*4);
lowPart &= ~(~0U << (sizeof(unsigned)*4));
highPart *= 10;
highPart += carry;
carry = highPart >> (sizeof(unsigned)*4);
highPart &= ~(~0U << (sizeof(unsigned)*4));
bigNumber[index] = lowPart | (highPart << (sizeof(unsigned)*4));
}
if (carry)
bigNumber.push_back(carry);
};
// here bigNumber should be a biginteger = currentNumber
for (int i = 0; i < bigNumber.size()*8*sizeof(unsigned); ++i) {
// looks for look consective bits set to '0'
bool hasFound = true;
for (int shift = 0; hasFound && shift < look; ++shift)
if (bigNumber[(i+shift)/(8*sizeof(unsigned))]
& (1U << ((i+shift) % (8*sizeof(unsigned)))) != 0)
hasFound = false;
if (hasFound) { // ok, bigNumber has look consecutive bits set to 0
// test if we are at the end of the bigNumber
int index = (i+look)/(8*sizeof(unsigned));
for (int j = ((i+look+8*sizeof(unsigned)-1) % (8*sizeof(unsigned)))+1;
j < (8*sizeof(unsigned)); j++)
if ((bigNumber[index] & (1U << j)) != 0)
return i; // the result is (currentNumber/(2^i));
while (++index < bigNumber.size())
if (bigNumber[index] != 0)
return i; // the result is (currentNumber/(2^i));
return -1;
};
};
return -1;
}
int main(int argc, char** argv) {
std::string val;
std::cin >> val;
std::cout << val << " is divided by 8 after " << ExistDigit(val, 3) << " bits." << std::endl;
return 0;
}
вы можете создать 'unsigned x' из' currentNumber', используя 'stringstream :: operator >>'. Извините, я не видел большую часть.Но затем, после вашего замечания: 'while (x% 8! = 0) x/= 2;'. – Franck
[FYI] Не используйте магические числа. если вы хотите вычесть «0» из чего-то, просто сделайте это как 'currentDigit - = '0';', и теперь ваш код сам документирует. – NathanOliver
@NathanOliver Спасибо, я не знал, что – MLaurentys