给定排好序的数组和一个数，从数组中找出最早出现该数的下标。
# coding: utf-8
# @author zhenzong
# @date 2018-05-06 18:49
def binary_search(array, target):
left, right = 0, len(array) - 1
while left < right:
mid = (left + right) >> 1
if array[mid] < target:
left = mid + 1
else:
right = mid
return right if array[right] == target else -1
print binary_search([1, 2, 3, 4, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 6, 7], 5)
print binary_search([1, 2, 3, 4, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 6, 7], 8)
print binary_search([1, 2, 3, 4, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 6, 7], 7)
print binary_search([1, 2, 3, 4, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 6, 7], 1)
# 输出
# 8
# -1
# 15
# 0
