[usaco]Your Ride Is Here题解

题目：

输入两个由大写字母组成的字符串，A~Z分别转换为1~26，然后将其累乘，得到的两个乘积如果mod 47后相等则输出GO，否则输出STAY

SAMPLE INPUT (file ride.in)

COMETQ
HVNGAT

OUTPUT FORMAT

A single line containing either the word "GO" or the word "STAY".

SAMPLE OUTPUT (file ride.out)

GO

OUTPUT EXPLANATION

Converting the letters to numbers:

C	O	M	E	T	Q
3	15	13	5	20	17
H	V	N	G	A	T
8	22	14	7	1	20

then calculate the product mod 47:

3 * 15 * 13 * 5 * 20 * 17 = 994500 mod 47 = 27
8 * 22 * 14 * 7 *  1 * 20 = 344960 mod 47 = 27

Because both products evaluate to 27 (when modded by 47), the mission is 'GO'.

题解：

乘积的取余等于取余的乘积，由此可以避免数据溢出。注意ASCII码和字符之间的转换，表内字符可以直接作为整数来计算，减去64即可。

代码：

/*
ID: xcwhkh1
LANG: C
TASK: ride
*/
#include <stdio.h>
char a[100002];
char b[100002];
int main () {
    FILE *fin  = fopen ("ride.in", "r");
    FILE *fout = fopen ("ride.out", "w");
    fscanf (fin, "%s\n%s",a,b); /* the two input integers */
    int sa=1,sb=1,i;
    for(i=0;a[i]!='\0';i++)
    sa=sa*(a[i]-64)%47;
    for(i=0;b[i]!='\0';i++)
    sb=sb*(b[i]-64)%47;
    if(sa!=sb)
    fprintf (fout,"STAY\n");
    else
    fprintf (fout,"GO\n");
    return 0;
}