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10-22-11-02-02-08.17.c
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10-22-11-02-02-08.17.c
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/* 10-22-11-02-02-08.17.c -- 第十章第二十二题 */
/* 有问题存在.主要,是为了体验分治算法的思想,沿着思路写出来了.说真的,对数字没有兴趣. - 01-03-16.06 */
#include <stdio.h>
#include <stdlib.h>
int main (void) ;
int multiplication (const int cardinal, const int multiplier) ;
int powBaseTen (const int power) ;
int main (void)
{
printf ("Is %d.\n", multiplication (54321, 12345)) ;
return 0 ;
}
int multiplication (const int cardinal, const int multiplier)
{
int temp, c_l, c_r, m_l, m_r, d1, d2, d3, c_lm_l, c_rm_r ;
int width_c, width_m ;
if (cardinal <= 10 || multiplier <= 10)
return cardinal * multiplier ;
else
{
for (width_c = 1, temp = 1; temp * 10 < cardinal; width_c++, temp *= 10)
NULL ;
c_l = cardinal / powBaseTen (width_c / 2) ;
c_r = cardinal - c_l * powBaseTen (width_c / 2) ;
for (width_m = 1, temp = 1; temp * 10 < multiplier; width_m++, temp *= 10)
NULL ;
m_l = multiplier / powBaseTen (width_m / 2) ;
m_r = multiplier - m_l * powBaseTen (width_m / 2) ;
d1 = c_l - c_r ;
d2 = m_r - m_l ;
c_lm_l = multiplication (c_l, m_l) ;
c_rm_r = multiplication (c_r, m_r) ;
d3 = multiplication (d1, d2) + c_lm_l + c_rm_r ;
return c_lm_l * powBaseTen (width_c) + d3 * powBaseTen (width_c / 2) + c_rm_r ;
}
}
int powBaseTen (const int power)
{
int result, i ;
if (power <= 0)
return 0 ;
for (i = 1, result = 10; i < power; i++)
result *= 10 ;
return result ;
}