201,600-degree star qualifying problem A (prefix product and inverse element)

　　Test instructions: Gives a string, each asking for x and y to calculate theproduct (mod9973) of the value (ASCII code value-28) of each character from X to Y.

Analysis: The first idea must be to figure out the prefix product for each location, and then just f[y]/f[x-1]. However, each prefix product has been mod9973, it can not directly come to the result, so the use of inverse element. Since A/b (mod p) p is an odd number, it is equivalent to A*INV (b) (mod p), so just save the prefix product and the inverse of the prefix product for each location.

But the topic has a pit point, if X and y beyond the position of this string, you can use the last data stored value instead of 0, because the topic given x and Y is not more than the length of the string, so every time I give the input data I memset again, resulting in this place WA several times.

At the same time, here is a trick is, since the inverse is mod9973, so as long as the storage of 0 to 9972 of the inverse to do a preprocessing can save a lot of time. See the code for details:

1#include <stdio.h>2#include <algorithm>3#include <string.h>4 using namespacestd;5 Const intMoD =9973;6 intInvintAintb//B is mod-27 {8     intans=1;9      while(b)Ten     { One         if(b&1) ans= (ans*a)%MoD; Ab>>=1; -a=a*a%MoD; -     } the     returnans; - } - Chars[100000+Ten]; - intnum[100000+Ten]; + intp[100000+Ten]; - intres[10000]; + intMain () A { at     intT; -      for (int i=1; i<mod;i++) RES[I]=INV (i,mod-2);  -      while(SCANF ("%d", &t) = =1) -     { -scanf"%s", s+1); -         intLen =strlen (s+1); in         //memset (num,0,sizeof (num)); -         //memset (P,0,sizeof (P)); tonum[0]=p[0]=1; +          for(intI=1; i<=len;i++) -         { thenum[i]=num[i-1]* (s[i]- -)%MoD; *             p[i]=Res[num[i]];  $         }Panax Notoginseng          while(t--) -         { the             intx, y; +scanf"%d%d",&x,&y); Aprintf"%d\n", num[y]*p[x-1]%MoD); the         } +     } -     return 0; $}

Note The code in the Red section.

201,600-degree star qualifying problem A (prefix product and inverse element)