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72 lines
2.2 KiB
C++
72 lines
2.2 KiB
C++
#include <iostream>
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using namespace std;
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int main()
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{
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cout << "Welcome to the Sieve of Sundaram\n" << endl;
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int arraySize;
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int numberPrimes = 0;
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cout << "Input a positive integer to find all the prime numbers up to and "
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<< "\nincluding that number: ";
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cin >> arraySize;
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int n = arraySize / 2;
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/* array to start off with that will eventually get
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all the composite numbers removed and the remaining
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ones output to the screen */
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int isPrime[arraySize + 1];
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for (int i = 0; i < n; ++i)
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{
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isPrime[i] = i;
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}
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for (int i = 1; i < n; i++)
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{
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for (int j = i; j <= (n - i) / (2 * i + 1); j++)
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{
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isPrime[i + j + 2 * i * j] = 0;/*From this list, remove all
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numbers of the form i + j + 2ij */
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}
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}
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int TheseArePrime = 0;
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if (arraySize > 2)
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{
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isPrime[TheseArePrime++] = 2;/*this IF statement adds 2 to the output */
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}
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for (int i = 1; i < n; i++)
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{
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if (isPrime[i] != 0)
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{
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isPrime[TheseArePrime++] = i * 2 + 1;
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}
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}
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int size = sizeof isPrime / sizeof(int);//total size of array/size of array data type
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for (int x = 0; x <= size; x++)
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{
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if (isPrime[x] != 0)
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{
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cout << isPrime[x] << "\t";//outputs all prime numbers found
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numberPrimes++;// the counter of the number of primes found
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}
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else
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{
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break;
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}
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}
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cout << "\nNumber of Primes: " << numberPrimes << endl;
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return 0;
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}
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/*
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Welcome to the Sieve of Sundaram
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Input a positive integer to find all the prime numbers up to and
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including that number: 10
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2 3 5 7
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Number of Primes: 4
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Welcome to the Sieve of Sundaram
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Input a positive integer to find all the prime numbers up to and
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including that number: 100
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2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97
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Number of Primes: 25
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