二分查找是比较常见的查找算法，在猜价的节目中就可以用到。 二分查找的时间复杂度为O(logn)。
Python实现：
迭代 def search(nums, target):
start = 0
end = len(nums) - 1
while start <= end:
mid = (start + end) // 2
mid_num = nums[mid]
if mid_num > target:
end = mid - 1
elif mid_num < target:
start = mid + 1
else:
return mid
return -1
递归 def search(nums, target, start, end):
if start > end:
return -1
mid = (start + end) // 2
mid_num = nums[mid] if mid_num > target:
return search(nums, target, start, mid-1)
elif mid_num < target:
return search(nums, target, mid+1, end)
else:
return mid
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