Guess Number Game

We are playing the Guess Game. The game is as follows:

I pick a number from 1 to n. You have to guess which number I picked.

Every time you guess wrong, I'll tell you whether the number is higher or lower.

You call a pre-defined API guess(int num) which returns 3 possible results (-1, 1, or 0):

Example

n = 10, I pick 4 (but you don't know)

Return 4. Correct !

注意计算中间节点的方法 (start+end)/2 和 start +(end-start)/2

前者对于Integer.MAX_VALUE溢出 后者ok

 /* The guess API is defined in the parent class GuessGame.
    @param num, your guess
    @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
       int guess(int num); */

 public class Solution extends GuessGame {
     /**
      * @param n an integer
      * @return the number you guess
      */
     public int guessNumber(int n) {
         // Write your code here
         int start = 1;
         int end = n;
         while(start<end){
             int mid = start+(end-start)/2;
             int res = guess(mid);
             if(res==0) return mid;
             else if(res==1) start = mid+1;
             else end = mid-1;
         }
         return start;
     }
 }