[LeetCode&Python] Problem 704. Binary Search

Posted 2021-01-30 chiyeung

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:

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

 

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