WeightedRandomNumber.cs

using UnityEngine;

public class WeightedRandomNumber {

	AnimationCurve _curve;
	float[] _cumulativeWeights;
	float _totalWeight;
	float _step;
	float _curveTime;

	public WeightedRandomNumber( AnimationCurve curve, int numSamples )
	{
		_curve = curve;
		_cumulativeWeights = new float[numSamples];
		_totalWeight = 0.0f;
		_step = 1.0f / numSamples;
		_curveTime = _curve[curve.length-1].time;
		for ( int i=0; i<numSamples; i++ )
		{
			var weight = _curve.Evaluate( _curveTime * i * _step + _step * .5f );
			_totalWeight += weight;
			_cumulativeWeights[i] = _totalWeight;
		}
	}

	public float Value()
	{
		var randWeight = Random.value * _totalWeight;
		var index = 0;
		while ( randWeight > _cumulativeWeights[index] )
			index++;

		return Random.Range( index * _step * _curveTime, (index + 1) * _step * _curveTime );
	}
}