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 = xmaxdiff = x-yfor 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]))