if ( ! function_exists( 'is_product_in_cart' ) ) {
	/**
	 * is_product_in_cart.
	 *
	 * @return bool
	 */
	function is_product_in_cart( $product_id ) {
		if ( 0 != $product_id ) {
			if ( isset( WC()->cart->cart_contents ) && is_array( WC()->cart->cart_contents ) ) {
				foreach ( WC()->cart->cart_contents as $cart_item_key => $cart_item_data ) {
					if (
						( isset( $cart_item_data['product_id'] )   && $product_id == $cart_item_data['product_id'] ) ||
						( isset( $cart_item_data['variation_id'] ) && $product_id == $cart_item_data['variation_id'] )
					) {
						return true;
					}
				}
			}
		}
		return false;
	}
}

You can add this snippet to your (child) theme's functions.php file.