Easy · System Design

Load balancer

Given an initial list of unique server names and a sequence of next/add/remove calls, implement a round-robin load balancer that walks the list with a cursor: nextServer() returns the server at the cursor and advances the cursor cyclically (nothing for an empty pool), addServer(name) appends a name that is not already in the list, and removeServer(name) deletes it without making any other server skip a turn. Return the servers handed out by the nextServer calls.

Examples

Example 1

{
  "servers": ["A", "B"],
  "ops": [
    {"kind": "next"},
    {"kind": "next"},
    {"kind": "next"},
    {"kind": "add", "server": "C"},
    {"kind": "next"}
  ]
}

Output: A, B, A, B

Example 2

{
  "servers": ["A", "B", "C"],
  "ops": [
    {"kind": "next"},
    {"kind": "next"},
    {"kind": "remove", "server": "A"},
    {"kind": "next"},
    {"kind": "remove", "server": "C"},
    {"kind": "next"},
    {"kind": "next"}
  ]
}

Output: A, B, C, B, B

Rebuild it in the studio

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