Project Euler Problem 25

问题：

The Fibonacci sequence is defined by the recurrence relation:

Fn = Fn1 + Fn2, where F1 = 1 and F2 = 1.

Hence the first 12 terms will be:

F1 = 1
F2 = 1
F3 = 2
F4 = 3
F5 = 5
F6 = 8
F7 = 13
F8 = 21
F9 = 34
F10 = 55
F11 = 89
F12 = 144

The 12th term, F12, is the first term to contain three digits.

What is the first term in the Fibonacci sequence to contain 1000 digits?

答案：4782

#include
char s1[1000]={0};
char s2[1000]={0};
void sum(char *s1, char *s2, int len)
{
    int flag=0, ex=0;
    int i = 0, k = 0;
    for (i=0; i    {
        k = (flag ? ex : 0) + s1[i]+ s2[i];
        if (k<10)
        {
            s1[i]=k;
            flag = 0;
        }else
        {
            s1[i] = k%10;
            flag=1;
            ex= k / 10;
        }
    }
}
int main(void)
{
    s1[0]=1;
    s2[0]=1;
    int i=2;
    while(++i)
    {
        if(i%2 == 1)
        {
            sum(s1,s2,1000);
            if(s1[999]) break;
        }
        else
        {
            sum(s2,s1,1000);
            if(s2[999]) break;
        }
    }
    printf("the first term in the Fibonacci sequence to contain 1000 digits is %d\n ", i);
    return 0;
}