Closest Prime Numbers in Range | Leetcode 2523

class Solution {
public:
    vector<int> closestPrimes(int left, int right) {
        //Apply sieve of eratosthenes
        vector<bool> isPrime(right+1,true);
        for(int i=2;i*i<=right;++i){
            if(isPrime[i]==true){
                for(int j=2;i*j<=right;++j)
                    isPrime[i*j]=false;
            }
        }
        //Save all the primes in our range
        vector<int> primes;
        for(int i=max(2,left);i<=right;++i){
            if(isPrime[i]==true)
                primes.push_back(i);
        }
        //Now find the 2 closest primes
        int a=0,b=INT_MAX;
        for(int i=1;i<primes.size();++i){
            if((b-a)>(primes[i]-primes[i-1])){
                b = primes[i];
                a = primes[i-1];
            }
        }
        //Build your answer
        vector<int> ans;
        if(a==0)    ans = {-1,-1};
        else        ans = {a,b};
        return ans;
    }
};