First Position of Target
For a given sorted array (ascending order) and a target number, find the first index of this number in O(log n) time complexity.
If the target number does not exist in the array, return -1.
Example
If the array is [1, 2, 3, 3, 4, 5, 10], for given target 3, return 2.
Solution
class Solution:
# @param nums: The integer array
# @param target: Target number to find
# @return the first position of target in nums, position start from 0
def binarySearch(self, nums, target):
if len(nums) == 0:
return -1
start, end = 0, len(nums) -1
while start + 1 < end:
mid = (start + end) / 2
if nums[mid] < target:
start = mid
else:
end = mid
if nums[start] == target:
return start
if nums[end] == target:
return end
return -1
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