Guess Number Higher or Lower Problem & Solution

We are playing the Guess Game. The game is as follows:

I pick a number from 1 to `n`. You have to guess which number I picked. Every time you guess wrong, I will tell you whether the number I picked is higher or lower than your guess. You call a pre-defined API `int guess(int num)`, which returns 3 possible results:

• -1: The number I picked is lower than your guess (i.e. `pick < num`).
• 1: The number I picked is higher than your guess (i.e. `pick > num`).
• 0: The number I picked is equal to your guess (i.e. `pick == num`).

Return the number that I picked.

C++ Solution

The runtime complexity of the algorithm is \$O(\log{}n)\$.

``````#pragma GCC optimize("Ofast")
#pragma GCC optimization("unroll-loops")

static const int _=[](){std::ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);return 0;}();

/**
* Forward declaration of guess API.
* @param  num   your guess
* @return 	     -1 if num is lower than the guess number
*			         1 if num is higher than the guess number
*               otherwise return 0
* int guess(int num);
*/
class Solution {
public:
int guessNumber(int n) {
int low = 1;
int high = n;
while (low < high) {
int mid = low + (high - low) / 2;
int result = guess(mid);

if (result == 0) {
return mid;
} else if (result > 0) {
low = mid + 1;
} else {
high = mid;
}
}

return low;
}
};
``````

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