70 lines
1.6 KiB
Go
70 lines
1.6 KiB
Go
package utils
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import (
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"errors"
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"math/rand"
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"time"
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)
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type weightedChooser struct {
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entries []interface{}
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weights []int
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totalWeight int
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rng *rand.Rand
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}
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func NewWeightedRandomChooser() *weightedChooser {
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src := rand.NewSource(time.Now().UTC().UnixNano())
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return &weightedChooser{
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rng: rand.New(src), // nolint:gosec
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}
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}
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func (w *weightedChooser) Put(value interface{}, weight int) {
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w.entries = append(w.entries, value)
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w.weights = append(w.weights, weight)
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w.totalWeight += weight
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}
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// GetAndRemove choose a random entry based on their weights, and removes it from the list
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func (w *weightedChooser) GetAndRemove() (interface{}, error) {
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if w.totalWeight == 0 {
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return nil, errors.New("cannot choose from zero weight")
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}
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i, err := w.weightedChoice()
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if err != nil {
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return nil, err
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}
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entry := w.entries[i]
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w.Remove(i)
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return entry, nil
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}
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// Based on https://eli.thegreenplace.net/2010/01/22/weighted-random-generation-in-python/
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func (w *weightedChooser) weightedChoice() (int, error) {
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rnd := w.rng.Intn(w.totalWeight)
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for i, weight := range w.weights {
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rnd -= weight
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if rnd < 0 {
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return i, nil
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}
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}
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return 0, errors.New("internal error - code should not reach this point")
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}
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func (w *weightedChooser) Remove(i int) {
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w.totalWeight -= w.weights[i]
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w.weights[i] = w.weights[len(w.weights)-1]
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w.weights = w.weights[:len(w.weights)-1]
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w.entries[i] = w.entries[len(w.entries)-1]
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w.entries[len(w.entries)-1] = nil
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w.entries = w.entries[:len(w.entries)-1]
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}
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func (w *weightedChooser) Size() int {
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return len(w.entries)
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}
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