Prime String..

Ankit has recently learned about ASCII values. He is very fond of experimenting. With his knowledge of ASCII values and character he has developed a special word and named it "Prime String" word.

A word that consists of alphabets whose ASCI values is a prime number is a Prime String word. An alphabet is Prime String alphabet if its ASCI value is prime.

Ankit's nature is to boast about the things he knows or has learned about. So just to defame his friends he gives few strings to his friends and asks them to convert them to the "Prime String" word. None of his friends would like to get insulted. Help them to convert the given strings to Prime String  Word.

Rules for converting:

1.Each character should be replaced by the nearest "Prime String" alphabet.

2.If the character is equidistant with 2 Prime alphabets. The one with a lower ASCII value will be considered as its replacement.

Example:

Input:  s = "abcd"
Output: aaae

Approach

C++

#include <bits/stdc++.h>
using namespace std;

bool prime[1001];
void primeInitialize()
{

    memset(prime, true, sizeof(prime));
    prime[0] = false;
    prime[1] = false;
    for (int i = 2; i * i <= 1000; i++)
    {
        if (prime[i])
        {
            for (int j = i * i; j <= 1000; j += i)
                prime[j] = false;
        }
    }
}
string primeString(string s)
{

    int n = s.size();
    for (int i = 0; i < n; i++)
    {
        int len = s[i];
        if (len < 97)
            s[i] = 'a';
        else if (prime[len] == false)
        {
            int j;
            int flag = 0, flag1 = 0;
            int x1, x2;
            for (j = len + 1; j <= 122; j++)
            {
                if (prime[j])
                {
                    flag = 1;
                    x1 = j;
                    break;
                }
            }
            int k;
            for (k = len - 1; k >= 97; k--)
            {
                if (prime[k])
                {
                    flag1 = 1;
                    x2 = k;
                    break;
                }
            }
            if (flag == 1 && flag1 == 1)
            {

                if (x1 - len < len - x2)
                    s[i] = x1;
                else
                    s[i] = x2;
            }
            else if (flag1 == 1 && flag == 0)
                s[i] = x2;
            else if (flag == 1 && flag1 == 0)
                s[i] = x1;
        }
    }
    return s;
}
int main()
{
    primeInitialize();
    string s = "abcd";

    cout << primeString(s) << "\n";

    return 0;
}