euler9

A Pythagorean triplet is a set of three natural numbers, a < b < c, for which,
a^2 + b^2 = c^2

For example, 3^2 + 4^2 = 9 + 16 = 25 = 5^2.

There exists exactly one Pythagorean triplet for which a + b + c = 1000.
Find the product abc.

#include <stdio.h>

#define N 1000
int main(int argc, const char *argv[])
{
    int a, b;

    for (a=1; a<N/3; a++) {
        for (b=N/3; b<(N-a);b++) {
            if ((a*a + b*b) == (N-a-b)*(N-a-b))
                goto end;
        }
    }

end:
    printf("a:%d, b:%d, c:%d product:%d\n", a, b, (N-a-b), a*b*(N-a-b));

    return 0;
}

利用交换律可以减少一些循环的次数。