HDOJ 1016 Prime Ring Problem(DFS深度优先搜索)

import java.util.Scanner;

public class Main{
private static boolean noPrimes[];

public static void main(String[] args) {
noPrimes = new boolean [40];
noPrimes[1] = true;
for (int i = 2; i < noPrimes.length; i++) {
if (noPrimes[i]) {
continue;
}
for (int j = i*2; j < noPrimes.length; j+=i) {
if (noPrimes[j]) {
continue;
}
noPrimes[j] = true;
}
}
int k = 1;
Scanner sc = new Scanner(System.in);
while (sc.hasNext()) {
int n = sc.nextInt();
int ans[] = new int
;
boolean used[] = new boolean[n+1];
used[1] = true;
ans[0] = 1;
System.out.println("Case "+k+":");
DFS(ans,used,1,n);
System.out.println();
k++;
}
sc.close();
}

private static void DFS(int[] ans, boolean[] used, int index, int n) {
if (index==n) {
System.out.print(ans[0]);
for (int i = 1; i < n; i++) {
System.out.print(" "+ans[i]);
}
Syste
4000
m.out.println();
}
for (int i = 2; i <= n; i++) {
if (!used[i]) {
if (noPrimes[i+ans[index-1]]) {
continue;
}
used[i] = true;
ans[index] = i;
if (index==n-1) {
if (noPrimes[ans[0] + ans[index]]) {
used[i] = false;
continue;
}
}
DFS(ans, used, index+1, n);//递推
used[i] = false;
}
}
}
}