題目：給定乙個有序的正數陣列arr和乙個正數range，如果可以自由選擇arr中的數字，想累加得到1～range範圍上所有的數，返回arr最少還缺幾個數
舉例：arr = [1,2,3,7] range = 15 1~15還缺14 返回1
arr = [1,5,7] range = 15 1~15還缺2和4 返回2
def needmins(arr,range_):
range = 0
needs = 0
for i in range(len(arr)):
if arr[i] > range + 1:
range = 2 * range + 1
needs += 1
if range > range_:
return needs
range += arr[i]
if range > range_:
return needs
while range_ > range + 1:
range = 2 * range + 1
needs += 1
return needs