374. Guess Number Higher or Lower.cpp

/** 
 * Forward declaration of guess API.
 * @param  num   your guess
 * @return       -1 if num is higher than the picked number
 *                1 if num is lower than the picked number
 *               otherwise return 0
 * int guess(int num);
 */
​
class Solution {
public:
    int guessNumber(int n) {
        int l=1,r=n;
        while(l<=r){
            int mid = l + (r-l)/2;
            int g = guess(mid);
            if(g==0)        return mid;
            else if(g>0)    l = mid+1;
            else            r = mid-1;
        }
        return -1;
    }
};