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problem008.cpp
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problem008.cpp
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#include <cstdlib>
#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
long long nextRun(const std::string& n, int digits, int* pos)
{
long long product = 1;
int c = 0;
int i = *pos;
for (; i < n.size(); ++i) {
if (n[i] == '0') {
product = 1;
c = 0;
} else {
product *= n[i] - '0';
if (++c == digits) {
break;
}
}
}
*pos = i;
return (c < digits) ? 0 : product;
}
long long greatestProduct(const std::string& n, int digits)
{
int i = 0;
long long current = nextRun(n, digits, &i);
long long max = current;
++i;
for (; i < n.size(); ++i) {
if (n[i] == '0') {
current = nextRun(n, digits, &i);
} else {
current /= n[i - digits] - '0';
current *= n[i] - '0';
}
if (current > max) {
max = current;
}
}
return max;
}
int main(int argc, char* argv[])
{
if (argc < 2) {
std::cout << "Usage: " << argv[0] << " <input>\n";
return 0;
}
std::ifstream file(argv[1]);
if (!file.is_open()) {
std::cerr << "Cannot open " << argv[1] << '\n';
return EXIT_FAILURE;
}
file.seekg(0, std::ios_base::end);
int bytes = file.tellg();
file.seekg(0, std::ios_base::beg);
std::string n;
n.reserve(bytes);
std::string line;
while (std::getline(file, line)) {
n.append(line);
}
std::cout << "Answer: " << greatestProduct(n, 13) << '\n';
return 0;
}