Saved from https://leetcode-cn.com/problems/guess-number-higher-or-lower/submissions/

guessNumber.cpp

// 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 s = 1, e = n;
        while (s < n) {
            int g = ((n - s) >> 1) + s;
            switch (guess(g)) {
            case -1:
                n = g - 1;
                break;
            case 1:
                s = g + 1;
                break;
            case 0:
                return g;
            }
        }
        return s;
    }
};