EasyLeetCode #704Binary Search

Binary Search

Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1.

Constraints

1 <= nums.length <= 10^4, -10^4 < nums[i], target < 10^4, All integers in nums are unique, nums is sorted in ascending order

Examples

Input: nums = [-1,0,3,5,9,12], target = 9

Output: 4

Solution

Approach

Classic binary search: repeatedly divide search space in half by comparing middle element with target.

def search(nums, target):
    left, right = 0, len(nums) - 1
    while left <= right:
        mid = (left + right) // 2
        if nums[mid] == target:
            return mid
        elif nums[mid] < target:
            left = mid + 1
        else:
            right = mid - 1
    return -1

Complexity

Time:O(log n)

Space:O(1)

Hints

1.Array is sorted, use binary search
2.Compare middle element with target
3.Adjust left or right pointer accordingly

Asked at

Google