[UVA] 151 - Power Crisis
Power Crisis
| Power Crisis |
During the power crisis in New Zealand this winter (caused by a shortage of rain and hence low levels in the hydro dams), a contingency scheme was developed to turn off the power to areas of the country in a systematic, totally fair, manner. The country was divided up into N regions (Auckland was region number 1, and Wellington number 13). A number, m, would be picked `at random', and the power would first be turned off in region 1 (clearly the fairest starting point) and then in every m'th region after that, wrapping around to 1 after N, and ignoring regions already turned off. For example, if N = 17 and m = 5, power would be turned off to the regions in the order:1,6,11,16,5,12,2,9,17,10,4,15,14,3,8,13,7.
The problem is that it is clearly fairest to turn off Wellington last (after all, that is where the Electricity headquarters are), so for a given N, the `random' number m needs to be carefully chosen so that region 13 is the last region selected.
Write a program that will read in the number of regions and then determine the smallest number m that will ensure that Wellington (region 13) can function while the rest of the country is blacked out.
Input and Output
Input will consist of a
series of lines, each line containing the number of regions (N) with
. The file will be terminated by a line consisting of
a single 0.
Output will consist of a series of lines, one for each line of the input. Each line will consist of the number m according to the above scheme.
Sample input
17 0
Sample output
7
#include <stdio.h>
#include <stdlib.h>
int Calu(int n, int k) {
static int link[101], i, j, head, prev, last;
for(i = 2; i < n; i++)
link[i] = i+1;
link[n] = 2, head = 2, prev = n;
for(i = 1; i < n; i++) {
for(j = 1; j < k; j++)
prev = head, head = link[head];
last = head;
link[prev] = link[head];
head = link[head];
}
if(last == 13) return 1;
return 0;
}
int main() {
int D[100], N, count, i;
for(i = 14; i < 100; i++) {
count = 2;
while(Calu(i, count) == 0) count++;
D[i] = count;
}
D[13] = 1;
while(scanf("%d", &N) == 1 && N) {
printf("%d\n", D[N]);
}
return 0;
}