"Huawei OJ" "074-Prime Companion"

"Huawei OJ" "Algorithm Total chapter" "Huawei OJ" "074-Prime Companion" "Project Download" topic description

    若两个正整数的和为素数，则这两个正整数称之为“素数伴侣”，如2和5、6和13，它们能应用于通信加密。现在密码学会请你设计一个程序，从已有的N（N为偶数）个正整数中挑选出若干对组成“素数伴侣”，挑选方案多种多样，例如有4个正整数：2，5，6，13，如果将5和6分为一组中只能得到一组“素数伴侣”，而将2和5、6和13编组将得到两组“素数伴侣”，能组成“素数伴侣”最多的方案称为“最佳方案”，当然密码学会希望你寻找出“最佳方案”。输入:    有一个正偶数N（N≤100），表示待挑选的自然数的个数。后面给出具体的数字，范围为[2,30000]。输出:    输出一个整数K，表示你求得的“最佳方案”组成“素数伴侣”的对数。

Enter a description

输入说明1 输入一个正偶数n2 输入n个整数

Output description

求得的“最佳方案”组成“素数伴侣”的对数。

Input example

42 5 6 13

Output example

2

Algorithm implementation

ImportJava.util.Arrays;ImportJava.util.Scanner;/** * Author: Wang Junshu * date:2016-01-06 10:43 * declaration:all rights Reserved!!! */ Public  class Main {     Public Static void Main(string[] args) {Scanner Scanner =NewScanner (system.in);//Scanner Scanner = new Scanner (Main.class.getClassLoader (). getResourceAsStream ("Data.txt"));         while(Scanner.hasnext ()) {intn = scanner.nextint ();int[] arr =New int[n]; for(inti =0; I < n;            i++) {Arr[i] = Scanner.nextint ();        } System.out.println (Countprimepairs (arr));    } scanner.close (); }Private Static Boolean IsPrime(intN) {if(N <2) {return false; }intsqrt = (int) math.sqrt (n); for(inti =2; I <= sqrt; i++) {if(n% i = =0) {return false; }        }return true; }/** * from behind * using dynamic programming to solve problems, dp[i] means (n-1) ~i The maximum number of companions; * When V[i]+v[j] is prime.     DP[I]+DP[J+1] = dp[i+1]+dp[j+1]+1;     * Due to the number of couples in pairs appear, must only in I-1 and j-1 on the basis of a pair. * When V[i]+v[j] is not a prime number. DP[I]=DP[I+1] * * @param v * @return  */    Private Static int Countprimepairs(int[] v) {int[] DP =New int[V.length +1]; for(inti = v.length-2; I >-1; i--) { for(intj = v.length-1; J > i; j--) {intCNT = IsPrime (V[i] + v[j])? (Dp[i +1]-Dp[j-1] + dp[j +1] +1): Dp[i +1]; Dp[i] = (cnt > dp[i])?            Cnt:dp[i]; }        }//System.out.println (arrays.tostring (v));//SYSTEM.OUT.PRINTLN (Arrays.tostring (DP));        returndp[0]; }}

"Huawei OJ" "074-Prime Companion"