python编程---example8

有一个数组，求其中两个数x,y，满足x的索引小于y的索引，使得 x-y 最大。

def max_drawdown(arr):
	assert len(arr)>2, "len(arr) should > 2!"
	x,y = arr[0:2]
	xmax = x
	maxdiff = x-y

	for i in range(2,len(arr)):
		if arr[i-1] > xmax:
			xmax = arr[i-1]
		if xmax - arr[i] > maxdiff:
			maxdiff = xmax - arr[i]
			x,y = xmax,arr[i]

	print("x=",x,",y=",y)
	return(maxdiff)

print(max_drawdown([3,7,2,6,4,1,9,8,5]))