用 0,1,2,3 \cdots 70,1,2,3?7 这 88 个数组成的所有整数中，质数有多少个（每个数字必须用到且只能用一次）。
提示：以 00 开始的数字是非法数字。
public class Main { static int[] a; static int count; public static void main(String[] args) { int n = 76543210; a = new int[n + 1]; for(int i = 2; i < a.length; i ++) a[i] = 1; for(int i = 2; i * i <= n; i ++) { if(a[i] == 1) { for(int j = i * i; j <= n; j += i) { a[j] = 0; } } } for(int i = 2; i < a.length; i ++) { if(a[i] == 1) { if(f(String.valueOf(i))) { count ++; System.out.println(i); } } } System.out.println(); System.out.println(count); } private static boolean f(String s) { int count = 0; int a = s.indexOf(‘0‘); int aa = s.indexOf(‘0‘) - s.lastIndexOf(‘0‘); int b = s.indexOf(‘1‘); int bb = s.indexOf(‘1‘) - s.lastIndexOf(‘1‘); int c = s.indexOf(‘2‘); int cc = s.indexOf(‘2‘) - s.lastIndexOf(‘2‘); int d = s.indexOf(‘3‘); int dd = s.indexOf(‘3‘) - s.lastIndexOf(‘3‘); int e = s.indexOf(‘4‘); int ee = s.indexOf(‘4‘) - s.lastIndexOf(‘4‘); int f = s.indexOf(‘5‘); int ff = s.indexOf(‘5‘) - s.lastIndexOf(‘5‘); int g = s.indexOf(‘6‘); int gg = s.indexOf(‘6‘) - s.lastIndexOf(‘6‘); int h = s.indexOf(‘7‘); int hh = s.indexOf(‘7‘) - s.lastIndexOf(‘7‘); int i = s.indexOf(‘8‘); int j = s.indexOf(‘9‘); if(a != -1) count ++; if(aa == 0) count ++; if(b != -1) count ++; if(bb == 0) count ++; if(c != -1) count ++; if(cc == 0) count ++; if(d != -1) count ++; if(dd == 0) count ++; if(e != -1) count ++; if(ee == 0) count ++; if(f != -1) count ++; if(ff == 0) count ++; if(g != -1) count ++; if(gg == 0) count ++; if(h != -1) count ++; if(hh == 0) count ++; if(i == -1) count ++; if(j == -1) count ++; if(count == 18) return true; else return false; } }
