[t103] Check Palindrome (Hard)

#include <stdio.h>
#include <ctype.h>
#include <string.h>

int main()
{
    char A[100010];
    scanf("%[^\n]", A);
    int n = strlen(A);
    int i = 0, j = n-1, c = 0;
    while (i < j) {
        if (!isalpha(A[i])) ++i;
        else if (!isalpha(A[j])) --j;
        else if (tolower(A[i]) != tolower(A[j])) {
            c = 0;
            break;
        }
        else ++i, --j, ++c;
    }
    if (c == 0) {
        printf("-\n");
        return 0;
    }
    for (int i = 0; c > 0; ++i) {
        if (isalpha(A[i])) {
            printf("%c", tolower(A[i]));
            --c;
        }
    }
    printf("\n");

    return 0;
}