I am developing a dapp in which I need to store large number of employee/customer name or id. Can I use array or map in my smart contract code? Will it increases the smart contract memory as number increase? Which one is the best suited way?
There is no limit on storing data in Blockchain, but the more data you store you will have to spend more money(in case of Livenet). However, in case of the private net, you may consider increasing gas price to store more data.
If the data you are trying to store is crucial and lot in quantity, I'd recommend you to use IPFS or Swarm. See this answer to understand more about it.
So basically, one of these help you keep data on a distributed file network, and data(files) on this network will be referenced by the addresses. Now you can add those references(addresses - hash) on the blockchain. It reduces your cost because your data is not on blockchain but only a reference to it.
Hope this helps.