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			42 lines
		
	
	
		
			1.0 KiB
		
	
	
	
		
			Go
		
	
	
	
	
	
			
		
		
	
	
			42 lines
		
	
	
		
			1.0 KiB
		
	
	
	
		
			Go
		
	
	
	
	
	
// Copyright 2019 The LevelDB-Go and Pebble Authors. All rights reserved. Use
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// of this source code is governed by a BSD-style license that can be found in
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// the LICENSE file.
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package randvar
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import "golang.org/x/exp/rand"
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// Weighted is a random number generator that generates numbers in the range
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// [0,len(weights)-1] where the probability of i is weights(i)/sum(weights).
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type Weighted struct {
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	rng     *rand.Rand
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	sum     float64
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	weights []float64
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}
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// NewWeighted returns a new weighted random number generator.
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func NewWeighted(rng *rand.Rand, weights ...float64) *Weighted {
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	var sum float64
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	for i := range weights {
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		sum += weights[i]
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	}
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	return &Weighted{
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		rng:     ensureRand(rng),
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		sum:     sum,
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		weights: weights,
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	}
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}
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// Int returns a random number in the range [0,len(weights)-1] where the
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// probability of i is weights(i)/sum(weights).
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func (w *Weighted) Int() int {
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	p := w.rng.Float64() * w.sum
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	for i, weight := range w.weights {
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		if p <= weight {
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			return i
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		}
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		p -= weight
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	}
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	return len(w.weights) - 1
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}
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