374. Guess Number Higher or Lower

 1 // Forward declaration of guess API.
 2 // @param num, your guess
 3 // @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
 4 int guess(int num);
 5 
 6 class Solution 
 7 {
 8 public:
 9     int guessNumber(int n) 
10     {
11         int left=1,right=n,mid=0;
12         while(left<right)
13         {
14             mid=left+(right-left)/2;
15             if(guess(mid)==1)
16                 left=mid+1;
17             else if(guess(mid)==-1)
18                 right=mid;
19             else
20                 return mid;
21         }
22         return left;
23     }
24 };