leetcode 374. Guess Number Higher or Lower

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):

-1 : My number is lower
 1 : My number is higher
 0 : Congrats! You got it!

Example:

n = 10, I pick 6.

Return 6.

# The guess API is already defined for you.
# @param num, your guess
# @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
# def guess(num):

class Solution(object):
    def guessNumber(self, n):
        """
        :type n: int
        :rtype: int
        """
        #1 <= x <= n
        i, j = 1, n
        while i<=j:
            mid = (i+j)>>1
            r = guess(mid)
            if r == 0:
                return mid
            elif r == 1:
                i = mid+1
            else:
                j = mid-1                
        #return -1?        

 注意："mid = (high + low) / 2;"

 lign + low => int + int --->it may cause overflow~
Interger scale [-2^31,2^31]

所以一般： int mid = start+(end-start)/2;

如果是c++代码要当心！