63 lines
1.7 KiB
C#
63 lines
1.7 KiB
C#
using System;
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namespace SemiColinGames {
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// A History is a queue of fixed length N that records the N most recent items Add()ed to it.
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// The mostly-recently-added item is found at index 0; the least-recently-added item is at index
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// N-1. Items older than the History's size are automatically dropped. The underlying
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// implementation is a fixed-size circular array; insertion and access are O(1).
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//
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// Example:
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// h = new History<int>(3);
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// h.Add(2); h.Add(3); h.Add(5);
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// Console.WriteLine("{0} {1} {2}", h[0], h[1], h[2]); // 5 3 2
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// h.Add(7);
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// Console.WriteLine("{0} {1} {2}", h[0], h[1], h[2]); // 7 5 3
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// h.Add(11); h.Add(13);
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// Console.WriteLine("{0} {1} {2}", h[0], h[1], h[2]); // 13 11 7
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class History<T> {
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// Backing store for the History's items.
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private readonly T[] items;
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// Points at the most-recently-inserted item.
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private int idx = 0;
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public History(int length) {
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items = new T[length];
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}
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public void Add(T item) {
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idx++;
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if (idx >= items.Length) {
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idx -= items.Length;
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}
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items[idx] = item;
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}
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public int Length {
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get => items.Length;
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}
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public T this[int age] {
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get {
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if (age < 0 || age >= items.Length) {
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throw new IndexOutOfRangeException();
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}
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int lookup = idx - age;
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if (lookup < 0) {
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lookup += items.Length;
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}
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return items[lookup];
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}
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}
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// This creates and populates a new array. It's O(n) and should probably only be used for tests.
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public T[] ToArray() {
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T[] result = new T[items.Length];
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for (int i = 0; i < items.Length; i++) {
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result[i] = this[i];
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}
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return result;
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}
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}
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}
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