Project Euler - Problem 11

#include<iostream>#include<fstream>#include<sstream>#include<math.h>#include<time.h>#include<string>using namespace std;int main(){double start = clock(),end(0);ifstream infile;infile.open("11.txt");if(!infile){cerr<<"can't open the file."<<endl;exit(1);}//将文件内容写入二维数组中int a[20][20];for (int l = 0; l<20; l++) {for (int r = 0; r<20 ; r++){infile >> a[l][r];}}int maxproduct = 0;for (int l = 0; l<20; l++) {for (int r = 0; r<20 ; r++){if(0 == a[l][r]) //排除为0的元素continue;int temp = 0;//横向if(r<=16){temp = a[l][r] * a[l][r+1] * a[l][r+2] * a[l][r+3];if(temp > maxproduct)maxproduct = temp;}//纵向if(l<=16){temp = a[l][r] * a[l+1][r] * a[l+2][r] * a[l+3][r];if(temp > maxproduct)maxproduct = temp;}//斜/向if(r<=16 && l<=16){temp = a[l][r] * a[l+1][r+1] * a[l+2][r+2] * a[l+3][r+3];if(temp > maxproduct)maxproduct = temp;}//斜/向if(r>=4 && l<=16){temp = a[l][r] * a[l+1][r-1] * a[l+2][r-2] * a[l+3][r-3];if(temp > maxproduct)maxproduct = temp;}}}cout << "the greatest product is "<< maxproduct << endl;end = clock();double runtime = (end - start)/1000;cout << "run time is " << runtime << endl;system("PAUSE");return 0;}