Given an array of integers nums sorted in ascending order, find the starting and ending position of a given target value.
Your algorithm’s runtime complexity must be in the order of O(log n).
If the target is not found in the array, return [-1, -1].
Linear scan array from left to right or from right to left.
Find the first index with given value. A trivial optimization here is when we find current element is greater than target(search left to right), we won’t search the left elements.
Time complexity: $O(N)$
Naive approach will not meet the challenge requirement. We can use the approach of binary search, but it’s a variant of original binary-search.
Take search first left position for example, When we got an index(suppose idx) where value equal target, we store the current position and safely ignore the right part
[idx ~ ..] of the array, so we update the
Search last right position is similar.
Time complexity: $O(logN)$.
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