This method checks perfect square in linear time

ValidPerfectSquare_v1.java

// this method will return 1 if N is valid perfect square number otherwise -1
public static int validPerfectSquare(int N) {
    if (N == 1)
        return 1;

    for (int i = 2; i <= N; i++) {
        if (i * i == N) {
            return 1;
        }
    }

    return -1;
}