DEV Community

Cover image for 34. Find First and Last Position of Element in Sorted Array
Harsh Rajpal
Harsh Rajpal

Posted on

34. Find First and Last Position of Element in Sorted Array

Problem Statement:

Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.

If target is not found in the array, return [-1, -1].

You must write an algorithm with O(log n) runtime complexity.

Example 1:
Input: nums = [5,7,7,8,8,10], target = 8
Output: [3,4]

Example 2:
Input: nums = [5,7,7,8,8,10], target = 6
Output: [-1,-1]

Example 3:
Input: nums = [], target = 0
Output: [-1,-1]

Constraints:

  • 0 <= nums.length <= 105
  • -109 <= nums[i] <= 109
  • nums is a non-decreasing array.
  • -109 <= target <= 109

Solution:
Algorithm:

  1. Find the target value in the array.
  2. If the target value is found,then find the first and last position of the target value.
  3. If the target value is not found,return [-1,-1].
  4. Return the result.

Code:

public class Solution {
    public int[] searchRange(int[] nums,int target){

        int[] result = new int[2];
        result[0] = -1;
        result[1] = -1;
        int left = 0;
        int right = nums.length - 1;
        int mid = 0;
        while(left <= right){
            mid = (left + right) / 2;
            if(nums[mid] == target){
                result[0] = mid;
                result[1] = mid;
                break;
            }
            else if(nums[mid] < target){
                left = mid + 1;
            }
            else{
                right = mid - 1;
            }
        }
        if(result[0] == -1){
            return result;
        }
        int i = mid - 1;
        while(i >= 0 && nums[i] == target){
            result[0] = i;
            i--;
        }
        i = mid + 1;
        while(i < nums.length && nums[i] == target){
            result[1] = i;
            i++;
        }
        return result;
    }

}
Enter fullscreen mode Exit fullscreen mode

Time Complexity:
O(log N)

Space Complexity:
O(1)

Image of Timescale

🚀 pgai Vectorizer: SQLAlchemy and LiteLLM Make Vector Search Simple

We built pgai Vectorizer to simplify embedding management for AI applications—without needing a separate database or complex infrastructure. Since launch, developers have created over 3,000 vectorizers on Timescale Cloud, with many more self-hosted.

Read more

Top comments (0)

Billboard image

The Next Generation Developer Platform

Coherence is the first Platform-as-a-Service you can control. Unlike "black-box" platforms that are opinionated about the infra you can deploy, Coherence is powered by CNC, the open-source IaC framework, which offers limitless customization.

Learn more

đź‘‹ Kindness is contagious

Please leave a ❤️ or a friendly comment on this post if you found it helpful!

Okay