Minimum number of guesses needed to find a specific number

Objective– Given the numbers 1 to 1000, what is the minimum number of guesses needed to find a specific number if you are given the hint “higher” or “lower” for each guesses you make.

Naive Approach: Linear search

Start guessing from 1 and then 2 then 3  …till we do not find the answer.

Time complexity: O(N) , N  = total numbers, as per our problem it is 1000.

Better Approach: Binary Search

Start from N/2 and keep on discarding half elements after each guess based on the hint. Let’s understand from one example.

N = 1 to 1024, specific no = 378

1st guess = 512, hint = lower, new N =1 to 512, discard numbers 513 to 1024.
2nd guess = 256, hint = higher, new N =257 to 512, discard numbers 1 to 256
3rd guess = 385, hint = lower, new N = 257 to 384, discard numbers 385 to 512
4th guess = 320, hint = higher, new N = 321 to 384, discard numbers 257 to 320
5th guess = 352, hint = higher, new N = 353 to 384, discard numbers 321 to 352
6th guess = 368, hint = higher, new N = 369 to 384, discard numbers 353 to 368
7th guess = 376, hint= higher, new N = 377 to 384, discard numbers 369 to 376
8th guess = 380, hint= lower, new N = 377 to 380, discard numbers 381 to 384
9th guess = 378 MATCH found

Total no of guesses = 9

Java Code:


Output:
No of guesses needed for N: 1024 and x: 378 are: 9

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If you find anything incorrect or you feel that there is any better approach to solve the above problem, please write comment.
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