题解 | #查找组成一个偶数最接近的两个素数#
查找组成一个偶数最接近的两个素数
https://www.nowcoder.com/practice/f8538f9ae3f1484fb137789dec6eedb9
题解：刚开始的思路是利用穷举法，将小于num的所有素数找出来，然后通过两层循环来遍历查找最接近的两个素数，很笨的方法，实现起来确实有点无脑。在参考了别人的代码后进行了优化，效果稍微能好一些。
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
Scanner scanner = new Scanner(br);
int num = scanner.nextInt();
int[] result = getTwoClosestPrimesFormAnEven2(num);
for (int i = 0; i < result.length; i++) {
System.out.println(result[i]);
}
}
// 参考别人的，优化后的方法
private static int[] getTwoClosestPrimesFormAnEven2(int num) {
if (num < 4 || num > 1000) return new int[0];
int[] result = new int[2];
int diff = num;
for (int i = 2; i <= num / 2; i++) {
// 主要是在这里进行了优化
if (isPrime(i) && isPrime(num-i)){
int value1 = i;
int value2 = num - i;
diff = (value2 -value1) < diff ? value2-value1 : diff;
result[0] = value1;
result[1] = value2;
}
}
return result;
}
// 自己写的未进行优化的方法
private static int[] getTwoClosestPrimesFormAnEven1(int num) {
if (num < 4 || num > 1000) return new int[0];
int[] result = new int[2];
StringBuilder builder = new StringBuilder();
for (int i = 2; i < num; i++) {
if (isPrime(i))
builder.append(i).append(" ");
}
String[] arr = builder.toString().trim().split(" ");
int diff = num;
for (int i = 0; i < arr.length-1 ; i++) {
for (int j = i; j < arr.length ; j++) {
Integer value1 = Integer.valueOf(arr[i]);
Integer value2 = Integer.valueOf(arr[j]);
if (value1 + value2 == num){
diff = (value2 - value1) < diff ? value2-value1:diff;
result[0] = value1;
result[1] = value2;
}
}
}
return result;
}
private static boolean isPrime(int num) {
boolean flag = true;
for (int i = 2; i <= num / 2; i++) {
if (num % i == 0)
flag = false;
}
return flag;
}
}
