高性能二分查找算法Python精简版

在已有排序的列表中，如果需要高性能查找特定数，使用二分查找；即使是无序列表，也可以先采用O(nlogn)时间复杂度下排序，再二分查找也是不错的选择

def binary_search(li, left, right, num):
    while left < right:
        mid = (left + right) // 2
        if li[mid] == num:
            return mid
        elif li[mid] > num:
            right = mid
        else:
            left = mid


if __name__ == '__main__':
    data = [e for e in range(1000)]
    res = binary_search(data, 0, len(data), 23)
    print(res, data[res])

 

功能：第一个大于等于target的位置：

# the first >= n position
def binary_search(nums, target):
    if not nums:
        return
    start, end = 0, len(nums)-1
    while start + 1 < end:
        mid = start + (end-start) // 2
        print(start, mid, end)
        if nums[mid] == target:
            end = mid
        elif nums[mid] > target:
            end = mid
        else:
            start = mid
    if nums[start] == target:
        return start
    if nums[end] == target:
        return end
data = [1,2,4,4,4,6,9,22]
print(binary_search(data, 4))

 

功能：第一个大于target的位置：

def binary_search(nums, target):
    if not nums:
        return
    start, end = 0, len(nums)-1
    while start + 1 < end:
        mid = start + (end-start) // 2
        print(start, mid, end)
        if nums[mid] == target:
            start = mid
        elif nums[mid] > target:
            end = mid
        else:
            start = mid
    if nums[start] == target:
        return start+1
    if nums[end] == target:
        return end + 1
data = [1,2,4,4,4,6,9,22]
print(binary_search(data, 4))