guess-number-higher-or-lower.cpp

// Time:  O(logn)
// Space: O(1)

// Forward declaration of guess API.
// @param num, your guess
// @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
int guess(int num);

class Solution {
public:
    int guessNumber(int n) {
        int left = 1, right = n;
        while (left <= right) {
            const auto mid = left + (right - left) / 2;
            if (guess(mid) <= 0) {
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }
        return left;
    }
};