58 lines
1.5 KiB
Dart
58 lines
1.5 KiB
Dart
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// help for the implementation from:
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// https://www.geeksforgeeks.org/program-to-find-the-nth-prime-number/
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// by Ujjwal Kumar Bhardwaj
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class NthPrime {
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// function to check if given number is prime or not
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// basic idea is number not divided by any primes are primes
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// bool isPrime(int k) {
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// // Corner cases
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// if (k <= 1) return false;
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// if (k == 2 || k == 3) return true;
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// // below 5 there are only two prime numbers 2 and 3
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// if (k % 2 == 0 || k % 3 == 0) return false;
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// // Using concept of prime number can be represented
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// // in form of (6*k + 1) or (6*k - 1)
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// for (int i = 5; i * i <= k; i = i + 6)
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// if (k % i == 0 || k % (i + 2) == 0) return false;
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// return true;
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// }
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// int prime(int n) {
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// if (n == 0) throw new ArgumentError('There is no zeroth prime');
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// int i = 2;
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// while (n > 0) {
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// // each time if a prime number is found decrease n
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// if (isPrime(i)) n--;
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// i++; // increase the integer and go ahead
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// }
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// i -= 1; // since decrement of k is being done before
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// // Increment of i, so i should be decreased by 1
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// return i;
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// }
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bool isPrime(int n) {
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for (int start = 2; start < n; start++) {
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if (n % start == 0) return false;
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}
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return true;
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}
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int prime(int n) {
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if (n == 0) throw new ArgumentError('There is no zeroth prime');
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int counter = 0, number = 2;
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for (; counter < n; number++) {
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if (isPrime(number)) counter++;
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}
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return --number;
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}
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}
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