Guessing a number knowing only if the number proposed is lower or higher?

Question

I need to guess a number. I can only see if the number I\'m proposing is lower or higher. Performance matters a whole lot, so I thought of the following algorithm:

Le

Answer 1

yes binary search is the most effective way of doing this. Binary Search is what you described. For a number between 1 and N Binary Search runs in O(log(n)) time.

So here is the algorithm to find a number between 1-N

int a = 1, b = n, guess = average of previous answers;

while(guess is wrong) {

    if(guess lower than answer) {a = guess;}
    else if(guess higher than answer) {b = guess;}

    guess = (a+b)/2;

} //Go back to while