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Concept

Overview

Halve the search space · then search answers, not arrays
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Concept
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1lo = 0, hi = n − 1        // candidates: arr[lo..hi]
2while lo ≤ hi:
3    mid = (lo + hi) / 2
4    if arr[mid] == target: found!
5    if arr[mid] <  target: lo = mid + 1
6    else:                  hi = mid − 1
7// each question halves the space → O(log n)
state
  • target9
  • n7

line 1Find 9 in a SORTED array. A linear scan checks one cell at a time — n questions worst case. Sortedness lets us ask a much better question: "is the middle too small or too big?"