we can safely treat as constant value and specify the dequeue operation as requiring constant time the disadvantage of this structure for the implementation of the priority queue is that the number of levels is fixed if an application requires priority queue with an unlimited number of priority levelsthen the vector or linked-list versions are better choice applicationcomputer simulations computers have long been used to model and simulate real-world systems and phenomena these simulations are simply computer applications that have been designed to represent and appropriately react to the significant events occurring in the system simulations can allow humans to study certain behaviors or experiment with certain changes and events in system to determine the appropriate strategy some of the more common simulations include weather forecasting and flight simulators flight simulatorwhich is mock-up of real cockpit and controlled by softwarehelps train pilots to deal with real situations without having to risk the life of the pilot or loss of the aircraft weather forecasts today are much more reliable due to the aide of computer simulations mathematical models have been developed to simulate weather patterns and atmospheric conditions these models can be solved using computer applicationswhich then provide information to meteorologists for use in predicting the weather computer simulations are also used for less glamorous applications businesses can use computer simulation to determine the number of employees needed to provide service to its customers for examplean airline may want to know how many ticket agents are needed at certain times of the day in order to provide timely service having too many agents will cost the airline moneybut too few will result in angry customers the company could simply study the customer habits at one airport and experiment with different number of agents at different times but this can be costly and time consuming in additionthe results may only be valid for that one airport to reduce the cost and allow for events that may occur at various airportsa computer simulation can be developed to model the real system airline ticket counter simulating an airline ticket counteror any other queuing system where customers stand in line awaiting serviceis very common queue structure is used to model the queuing system in order to study certain behaviors or outcomes some of the typical results studied include average waiting time and average queue length queuing systems that use single queue are easier to model more complex systems like those representing grocery store that use multiple queuesrequire more complex models in this textwe limit our discussion to single-queue systems