挑战程序竞赛系列（44）：4.1计数 欧拉函数

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挑战程序竞赛系列（44）：4.1计数 欧拉函数

详细代码可以fork下Github上leetcode项目，不定期更新。

练习题如下：

• POJ 2407: Relatives

POJ 2407: Relatives

条件解析：

a=xz and b=xy,不存在x>1,z>0,y>0

a = xz space and space b = xy, 不存在x > 1, z > 0, y > 0

说白了，两两互素，比如 a = 4， b = 9

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.StringTokenizer;

public class Main{

    String INPUT = "./data/judge/201709/P2407.txt";

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

    static final int MAX_N = 10000   16;
    int[] euler = new int[MAX_N];

    public void euler_phi(){
        for (int i = 0; i < MAX_N;   i) euler[i] = i;
        for (int i = 2; i < MAX_N;   i){
            if (euler[i] == i){
                for (int j = i; j < MAX_N; j  = i){
                    euler[j] = euler[j] / i * (i - 1);
                }
            }
        }
    }

    public int phi(int n){
        int res = n;
        for (int i = 2; i < n / i;   i){
            if (n % i == 0){
                res = res / i * (i - 1);
                for (; n % i == 0; n /= i);
            }
        }
        if (n != 1){
            res = res / n * (n - 1);
        }
        return res;
    }

    void solve() {

        euler_phi();

        while (true){
            int n = ni();
            if (n == 0) break;
            if (n < MAX_N)
                out.println(euler[n]);
            else
                out.println(phi(n));
        }
    }

    FastScanner in;
    PrintWriter out;

    void run() throws IOException {
        boolean oj;
        try {
            oj = !System.getProperty("user.dir").equals("F:\java_workspace\leetcode");
        } 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();
        solve();
        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);
        }
    }
}

啧啧，睡了一觉回来，跑不快了。。。

github fork leetcode space

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