POJ 刷题系列：2739. Sum of Consecutive Prime Numbers

POJ 刷题系列：2739. Sum of Consecutive Prime Numbers

传送门：POJ 2739. Sum of Consecutive Prime Numbers

题意：

给定一个数num，求连续的素数和等于num的个数。

思路： 题目给定了连续素数，所以只需要从小于num的素数开始不断累加，知道sum >= num，其中若sum == num则计数。素数打表采用艾氏筛选法。

代码如下：

代码语言：javascript复制

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Map;
import java.util.StringTokenizer;

public class Main{

    String INPUT = "./data/judge/201712/P2739.txt";

    public static void main(String[] args) throws IOException {
        new Main().run();
    }

    static final int MAX_N = 10000   16;

    int[] prime = new int[MAX_N];
    boolean[] isPrime = new boolean[MAX_N];
    int tot;

    void sieve() {
        Arrays.fill(isPrime, true);
        for (int i = 2; i < MAX_N;   i) {
            if (isPrime[i]) {
                prime[tot  ] = i;
                for (int j = 2 * i; j < MAX_N; j  = i) {
                    isPrime[j] = false;
                }
            }
        }
    }


    int solve(int num) {
        int count = 0;
        for (int i = 0; i < tot;   i) {
            if (prime[i] > num) break;
            int j = i;
            int sum = 0;
            while (sum < num) {
                sum  = prime[j  ];
            }
            if (sum == num) count  ;
        }
        return count;
    }

    void read() {
        sieve();
        while (true) {
            int num = ni();
            if (num == 0) break;
            out.println(solve(num));
        }
    }

    FastScanner in;
    PrintWriter out;

    void run() throws IOException {
        boolean oj;
        try {
            oj = ! System.getProperty("user.dir").equals("F:\oxygen_workspace\Algorithm");
        } catch (Exception e) {
            oj = System.getProperty("ONLINE_JUDGE") != null;
        }

        InputStream is = oj ? System.in : new FileInputStream(new File(INPUT));
        in = new FastScanner(is);
        out = new PrintWriter(System.out);
        long s = System.currentTimeMillis();
        read();
        out.flush();
        if (!oj){
            System.out.println("["   (System.currentTimeMillis() - s)   "ms]");
        }
    }

    public boolean more(){
        return in.hasNext();
    }

    public int ni(){
        return in.nextInt();
    }

    public long nl(){
        return in.nextLong();
    }

    public double nd(){
        return in.nextDouble();
    }

    public String ns(){
        return in.nextString();
    }

    public char nc(){
        return in.nextChar();
    }

    class FastScanner {
        BufferedReader br;
        StringTokenizer st;
        boolean hasNext;

        public FastScanner(InputStream is) throws IOException {
            br = new BufferedReader(new InputStreamReader(is));
            hasNext = true;
        }

        public String nextToken() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (Exception e) {
                    hasNext = false;
                    return "##";
                }
            }
            return st.nextToken();
        }

        String next = null;
        public boolean hasNext(){
            next = nextToken();
            return hasNext;
        }

        public int nextInt() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Integer.parseInt(more);
        }

        public long nextLong() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Long.parseLong(more);
        }

        public double nextDouble() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Double.parseDouble(more);
        }

        public String nextString(){
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return more;
        }

        public char nextChar(){
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return more.charAt(0);
        }
    }

    static class D{

        public static void pp(int[][] board, int row, int col) {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < row;   i) {
                for (int j = 0; j < col;   j) {
                    sb.append(board[i][j]   (j   1 == col ? "n" : " "));
                }
            }
            System.out.println(sb.toString());
        }

        public static void pp(char[][] board, int row, int col) {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < row;   i) {
                for (int j = 0; j < col;   j) {
                    sb.append(board[i][j]   (j   1 == col ? "n" : " "));
                }
            }
            System.out.println(sb.toString());
        }
    }

    static class ArrayUtils {

        public static void fill(int[][] f, int value) {
            for (int i = 0; i < f.length;   i) {
                Arrays.fill(f[i], value);
            }
        }

        public static void fill(int[][][] f, int value) {
            for (int i = 0; i < f.length;   i) {
                fill(f[i], value);
            }
        }

        public static void fill(int[][][][] f, int value) {
            for (int i = 0; i < f.length;   i) {
                fill(f[i], value);
            }
        }
    }

    static class Num{
        public static <K> void inc(Map<K, Integer> mem, K k) {
            if (!mem.containsKey(k)) mem.put(k, 0);
            mem.put(k, mem.get(k)   1);
        }
    }
}

numbers sum

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