云网络双11优惠活动

def validate_coupon(coupon_code, order_total):
    valid_coupons = {
        "SAVE10": 0.10,  # 10% off
        "FREESHIP": 0    # Free shipping
    }
    
    if coupon_code in valid_coupons:
        discount = valid_coupons[coupon_code]
        if discount == 0:  # Special case for free shipping
            return "Free shipping applied."
        else:
            discounted_total = order_total * (1 - discount)
            return f"Discounted total: {discounted_total:.2f}"
    else:
        return "Invalid coupon code."

# Example usage
print(validate_coupon("SAVE10", 100))  # Should apply a 10% discount
print(validate_coupon("FREESHIP", 50))  # Should apply free shipping
print(validate_coupon("INVALID", 75))  # Should indicate invalid coupon