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;
    }
}