import numpy as np


def mean_square_error(y_true: np.ndarray, y_pred: np.ndarray) -> float:
    """
    Calculate MSE loss

    Parameters
    ----------
    y_true: ndarray of shape (n_samples, )
        True response values
    y_pred: ndarray of shape (n_samples, )
        Predicted response values

    Returns
    -------
    MSE of given predictions
    """
    return np.mean(np.square(y_true - y_pred))


def misclassification_error(y_true: np.ndarray, y_pred: np.ndarray, normalize: bool = True) -> float:
    """
    Calculate misclassification loss

    Parameters
    ----------
    y_true: ndarray of shape (n_samples, )
        True response values
    y_pred: ndarray of shape (n_samples, )
        Predicted response values
    normalize: bool, default = True
        Normalize by number of samples or not

    Returns
    -------
    Misclassification of given predictions
    """
    mult = y_true * y_pred
    if normalize:
        return np.sum(mult < 0, axis=0) / mult.shape[0]
    else:
        np.sum(mult < 0, axis=0)


def accuracy(y_true: np.ndarray, y_pred: np.ndarray) -> float:
    """
    Calculate accuracy of given predictions

    Parameters
    ----------
    y_true: ndarray of shape (n_samples, )
        True response values
    y_pred: ndarray of shape (n_samples, )
        Predicted response values

    Returns
    -------
    Accuracy of given predictions
    """
    pred_num = y_pred.shape[0]
    correct_num = len([1 for i in range(pred_num) if y_pred[i] == y_true[i]])
    return correct_num / pred_num


def cross_entropy(y_true: np.ndarray, y_pred: np.ndarray) -> float:
    """
    Calculate the cross entropy of given predictions

    Parameters
    ----------
    y_true: ndarray of shape (n_samples, )
        True response values
    y_pred: ndarray of shape (n_samples, )
        Predicted response values

    Returns
    -------
    Cross entropy of given predictions
    """
    raise NotImplementedError()
