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:

Find the target value in the array.
If the target value is found,then find the first and last position of the target value.
If the target value is not found,return [-1,-1].
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;
    }

}

Time Complexity:
O(log N)

Space Complexity:
O(1)

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

Harsh Rajpal

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