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  • Almost Prime

    Description
    Almost Prime
    time limit per test: 2 seconds
    memory limit per test: 256 megabytes
    input: standard input
    output: standard output

    A number is called almost prime if it has exactly two distinct prime divisors. For example, numbers 6, 18, 24 are almost prime, while 4, 8, 9, 42 are not. Find the amount of almost prime numbers which are between 1 and n, inclusive.

    Input

    Input contains one integer number n (1 ≤ n ≤ 3000).

    Output

    Output the amount of almost prime numbers between 1 and n, inclusive.

    Sample test(s)
    input
    10
    output
    2
     
     
     
     
     
     
    input
    21
    output
    8
     
     
     
     
     
     
    题解:
      素因子数的种类有且只有两种,称为Almost Prime。
           例如:18=2*3*3,只有2和3,是Almost Prime。
           求1~n Almost Prime 数量。
    代码:
     1 #include <iostream>
     2 #include <cstdio>
     3 
     4 using namespace std;
     5 //计算数字n不同素因子个数
     6 int distinctPrime (int n);
     7 
     8 int main()
     9 {
    10     int n, i, counter = 0;
    11     cin >> n;
    12     for(i=1; i<=n; i++){
    13         if(distinctPrime(i) == 2)
    14             counter ++;
    15     }
    16     cout << counter <<endl;
    17     return 0;
    18 }
    19 
    20 int distinctPrime (int n) {
    21     int i, t, flag, counter = 0;
    22     for(i=2, t=n; i<n; i++) {
    23         while(t>0) {
    24             if(t%i==0)
    25                 t = t/i;
    26             else
    27                 break;
    28             flag = 1;
    29         }
    30         if(flag)
    31             counter++;
    32         flag = 0;
    33     }
    34     return counter;
    35 }

    Problem -26A - Codeforces

    转载请注明出处:http://www.cnblogs.com/michaelwong/p/4133164.html

     
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  • 原文地址:https://www.cnblogs.com/michaelwong/p/4133164.html
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