Palindrome quiz

#include <cstdio>
#include <cctype>
#include <vector>

using namespace std;


int main() {
    vector<char> book;

    for (char c; scanf("%c", &c) == 1;) {
        if (isalpha(c)) {
            book.push_back(tolower(c));
        }
    }

    int i = 0;
    int j = book.size() - 1;

    while (i < j) {
        if (book[i] != book[j]) {
            printf("NO\n");
            return 0;
        }

        i++;
        j--;
    }

    printf("YES\n");

    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED