根据离散概率随机返回数组中的项

a[] :

0	1	2	3
0.1	0.2	0.3	0.4

 

cumsums[]:(cumsums[i]表示返回值小于i的概率)

0	1	2	3	4
0.0	0.1	0.3	0.6	1.0

static double cumsums[];

void GetCumsums(double a[],double cumsums[],int length) (length=5)
{
	cumsums[0] = 0.0;

	for(int index = 1;index < length;index++)
	{
		cumsums[index] = cumsums[index - 1] + a[index - 1];
	}
}

int Discrete(double cumsums[],int length)
{
	double probability = ((double)rand()) / RAND_MAX;
	
	int low = 0;
	int high = length - 1;
	int middle;

	while(low + 1 < high)
	{
		middle = (low + high) / 2;

		if(cumsums[middle] < probability)
		{
			low = middle;
		}
		else
		{
			high = middle;
		}
	}

	return low;