二分查找为什么不能使用(left+right)/2？

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32    /** 
 * 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);
 */

//二分查找
public class Solution extends GuessGame {
    public int guessNumber(int n) {
        int left = 1;
        int right = n;
        while(left <= right){
            int mid = left + (right - left)/2 <= right;
            //int mid = (left+right)/2;
            int result = guess(mid);
            if(result == 0){
                return mid;
            }
            else if(result == -1){
                right = mid - 1;
            }
            else if(result == 1){
                left = mid + 1;
            }
        }
        return -1;
    }
}