3115. Maximum Prime Difference

C++

class Solution {
public:
    bool isPrime(const int& x) {
        if (x < 2) return false;
        if (x < 4) return true;
        if (x % 2 == 0 || x % 3 == 0) return false;

        const int range = sqrt(x) + 1;
        for (int i = 5; i < range; ++i) {
            if (x % i == 0 || x % (i + 2) == 0) return false;
        }

        return true;
    }

    int maximumPrimeDifference(vector<int>& nums) {
        int front = 0;
        // Find front
        for(int i = 0; i < nums.size(); ++i) {
            if (isPrime(nums[i])) {
                front = i;
                break;
            }
        }
        int back = front;
        // Find back
        for (int i = nums.size() - 1; i > front; --i) {
            if (isPrime(nums[i])) {
                back = i;
                break;
            }
        }

        return back - front;
    }
};