704. Binary Search-二分查找

Given a sorted (in ascending order) integer array nums of n elements and a target value, write a function to search target in nums. If target exists, then return its index, otherwise return -1.

Example 1:
Input: nums = [-1,0,3,5,9,12], target = 9
Output: 4
Explanation: 9 exists in nums and its index is 4

Example 2:
Input: nums = [-1,0,3,5,9,12], target = 2
Output: -1
Explanation: 2 does not exist in nums so return -1

Note:

• You may assume that all elements in nums are unique.
• n will be in the range [1, 10000].
• The value of each element in nums will be in the range [-9999, 9999].

Solution in python:
1.Package function

class Solution:
    def search(self, nums: List[int], target: int) -> int:
        try:
            return nums.index(target)
        except BaseException:
            return -1

2.Binary search

class Solution:
    def search(self, nums: List[int], target: int) -> int:
        def binarysearch(nums, target, left, right):
            mid = (left+right)//2
            if left <= right:   
                if nums[mid] < target:
                    return binarysearch(nums, target, mid+1, right)
                elif nums[mid] > target:
                    return binarysearch(nums, target, left, mid-1)
                else:
                    return mid
            else:
                return -1
        return binarysearch(nums, target, 0, len(nums)-1)