Project Euler Problem 4

问题：

A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 99.

Find the largest palindrome made from the product of two 3-digit numbers.

答案： 906609

#include

int reverse(int n)
{
    int reversed = 0;
    while(n>0){
        reversed = 10*reversed + n%10;
        n /= 10;
    }

    return reversed;
}

int isPalindrom(int n)
{
    return n==reverse(n);
}

int main(void)
{
    int largest = 0;
    int a = 999;
    int b = 999;
    int db = 1;

    while(a>=100){
        if((a%11) == 0)
            b = 999, db = 1;
        else
            b = 990, db = 11;

        while(b>=a){
            if(a*b < largest)
                break;
            if(isPalindrom(a*b))
                largest = a*b;
            b -= db;
        }
        a--;
    }

    printf("%d\n", largest);
    return 0;
}