Potentiometers

ACCEPTED !! Another one from Dhaka regionals 2006/07
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Question: Potentiometers
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#include "iostream.h"
#include "math.h" 

int main()
{

   int t = 1;
   while(1) {
       int n;
       cin >> n;
       if(n == 0) break;
       if(t > 1) cout << endl;
       int parr[n];
       int r = ceil(sqrt(n));
       int c = sqrt(n);
       int sparr[r];
       for(int i = 0; i < r; i++) sparr[i] = 0;
       for(int i = 0; i < n; i++) {
           cin >> parr[i];
           sparr[i/c] += parr[i];
       }
       cout << "Case " << t << ":\n";
       while(1) {
           char command[4];
           cin >> command;
           if(strcmp(command, "END") == 0) break;
           if(strcmp(command, "S") == 0) {
               int x, r;
               cin >> x >> r;
               x--;
               sparr[x/c] += r - parr[x];
               parr[x] = r;
           }
           else if(strcmp(command, "M") == 0) {
               int x, y;
               cin >> x >> y;
               x--;
               y--;
               int sr = x/c;
               int er = y/c;
               int res = 0;
               for(int i = sr; i < er; i++) res += sparr[i];
               for(int i = sr*c; i < x; i++) res -= parr[i];
               for(int i = er*c; i <= y; i++) res += parr[i];
               cout << res << endl;
           }
       }
       t++;
   }
   return 0;
}

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