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Nearest prime less than given number n C++
We are given a number n, we need to find the nearest prime number that is less than n. We can find the number easily if we start checking from the n - 1. Let's see some examples.
Input
10
Output
7
Algorithm
- Initialise the number n.
- Write a loop that iterates from n - 1 to 1
- Return the first prime number that you found
- Return -1 if you didn't find any prime that's less than given n
Implementation
Following is the implementation of the above algorithm in C++
#include <bits/stdc++.h>
using namespace std;
bool isPrime(int n) {
if (n == 2) {
return true;
}
for (int i = 2; i <= ceil(sqrt(n)); i++) {
if (n % i == 0) {
return false;
}
}
return true;
}
int getNearestPrimeNumber(int n) {
for (int i = n - 1; i > 1; i--) {
if (isPrime(i)) {
return i;
}
}
return -1;
}
int main() {
int n = 20;
cout << getNearestPrimeNumber(n) << endl;
return 0;
}Output
If you run the above code, then you will get the following result.
19
Updated on: 23-Oct-2021
1K+ Views
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