374_Guess Number Higher or Lower.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 i=1;
        int j=n;
        
        while(i<j){
            int mid=i+(j-i)/2;
            int res=guess(mid);
            if(res==0)
                return mid;
            else if(res<0){
                j=mid-1;
            }
            else{
                i=mid+1;
            }
        }
        
        return i;
    }
};