Prime Cuts
A prime number is a counting number ( tex2html_wrap_inline26 ) that is evenly divisible only by 1 and itself. In this problem you are to write a program that will cut some number of prime numbers from the list of prime numbers between (and including) 1 and N. Your program will read in a number N; determine the list of prime numbers between 1 and N; and print the C*2 prime numbers from the center of the list if there are an even number of prime numbers or (C*2)-1 prime numbers from the center of the list if there are an odd number of prime numbers in the list.
Input
Each input set will be on a line by itself and will consist of 2 numbers. The first number ( tex2html_wrap_inline38 ) is the maximum number in the complete list of prime numbers between 1 and N. The second number ( tex2html_wrap_inline42 ) defines the C*2 prime numbers to be printed from the center of the list if the length of the list is even; or the (C*2)-1 numbers to be printed from the center of the list if the length of the list is odd.
Output
For each input set, you should print the number N beginning in column 1 followed by a space, then by the number C, then by a colon (:), and then by the center numbers from the list of prime numbers as defined above. If the size of the center list exceeds the limits of the list of prime numbers between 1 and N, the list of prime numbers between 1 and N (inclusive) should be printed. Each number from the center of the list should be preceded by exactly one blank. Each line of output should be followed by a blank line. Hence, your output should follow the exact format shown in the sample output.
Sample Input
21 2
18 2
18 18
100 7
Sample Output
21 2: 5 7 11↵\r\n
↵\r\n
18 2: 3 5 7 11↵\r\n
↵\r\n
18 18: 1 2 3 5 7 11 13 17↵\r\n
↵\r\n
100 7: 13 17 19 23 29 31 37 41 43 47 53 59 61 67↵\r\n
↵\r\n
注意事項:
1.讀取資料輸入直到結束
int max,amount;
while(scanf("%d %d",&max, &amount)!=EOF){
...
}
2.找出範圍內的質數(題目定義質數包含1)，並將這些質數存放在array當中
int prime[max];
prime[1]=1;
prime[2]=2;
count=2;
//find the prime list
for(int num=3;num<=max;num+=2){
is_prime=1;
for(int j=2;j<num;j++){
if((num%j)==0 && (j!=num)){
is_prime=0;
break;
}
}
if(is_prime){
count++;
prime[count]=num;
}
}
3.找出要需要列印出來的質數的位置:
if(count%2==0){
center = count/2;
start = center-amount+1;
end = center+amount;
}else{
center = count/2+1;
start = center-amount+1;
end = center+amount-1;
}
4.若是要列印出來的質數數量超過範圍讀處理方式:
if(start<=0)start=1;
if(end>=count)end=count;
5.將題目所需要的質數列印出來:
for(int k=start;k<=end;k++){
printf(" %d",prime[k]);
}
Code:
#include <stdio.h>
#include <math.h>
int main(void){
int max,amount;
while(scanf("%d %d",&max, &amount)!=EOF){
int prime[max];
printf("%d %d:",max,amount);
for(int i=1;i<max;i++){
prime[i]=0;
}
int is_prime,count;
int start,center,end;
prime[1]=1;
prime[2]=2;
count=2;
//find the prime list
for(int num=3;num<=max;num+=2){
is_prime=1;
for(int j=2;j<num;j++){
if((num%j)==0 && (j!=num)){
is_prime=0;
break;
}
}
if(is_prime){
count++;
prime[count]=num;
}
}
//for(int l=1;l<=count;l++) printf("%d.%d\n",l,prime[l]);
//check the how many and the site to print out.
if(count%2==0){
center = count/2;
start = center-amount+1;
end = center+amount;
}else{
center = count/2+1;
start = center-amount+1;
end = center+amount-1;
}
//for the exception situations
if(start<=0)start=1;
if(end>=count)end=count;
//show the result
for(int k=start;k<=end;k++){
printf(" %d",prime[k]);
}
//printf(",count=%d,center=%d,start=%d,end=%d",count,center,start,end);
printf("\n\n");
}
return 0;
}
