Binary Search

Binary Search

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].

Solutions

🧠 Cpp

class Solution
{
public:
    //classic O(log n) solution
    int search(vector<int>& nums, int target)
    {
        if(nums.empty())
            return -1;
        //starting index is in the middle of the array
        //manipulate indexies
        int pos_a = 0, pos_b = nums.size()-1;
        while (pos_a <= pos_b)
        {
            size_t mid = (pos_a+pos_b) / 2;
            if(nums[mid] == target)
                return mid;
            else if(nums[mid] < target)
                pos_a = mid + 1;
            else
                pos_b = mid - 1;
        }

        return -1;
    }
};