704. 二分查找

  

通常可以写出的二分法：mid = (start + end) / 2;

另一种写法：mid = start + (end - start) / 2，可防止 (start + end) 溢出。

代码一：

class Solution(object):
    def search(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: int
        """
        if target in nums:
            return nums.index(target)
        else:
            return -1

代码二：

class Solution(object):
    def search(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: int
        """
        i, j = 0, len(nums)-1

        while i <= j:
            mid = int((i+j) / 2)
            if nums[mid] == target:
                return mid
            elif nums[mid] < target:
                i = mid+1
            else:
                j = mid-1
        return -1

代码三：

class Solution(object):
    def search(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: int
        """
        i, j = 0, len(nums)-1
        if i == j and nums[i] == target:
            return i
        while i <= j:
            mid = i + int((j - i) / 2)
            if nums[mid] == target:
                return mid
            elif nums[mid] < target:
                i = mid+1
            else:
                j = mid-1
        return -1