Find First and Last Position of Element in Sorted Array Solution - The Coding Shala

Home >> Interview Prep >> Find first and the last position of an element in a sorted array

 In this post, we will learn how to Find the First and Last Position of Element in Sorted Array and will implement its solution in Java.

Find First And Last Position of Element in Sorted Array Problem

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

If the 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]

Find First and Last Position of Element in Sorted Array Java Solution

Approach 1

Using Binary Search.

Time complexity: O(log n)

Java Program: 

class Solution {
    public int[] searchRange(int[] nums, int target) {
        int[] result = new int[2];
        result[0] = findFirst(nums, target);
        result[1] = findLast(nums, target);
        return result;
    }
    
    int findFirst(int[] nums, int target) {
        int index = -1;
        int start = 0;
        int end = nums.length - 1;
        while (start <= end) {
            int mid = start + (end - start) / 2;
            if (nums[mid] >= target) end = mid - 1;
            else start = mid + 1;
            
            if (nums[mid] == target) index = mid;
        }
        return index;
    }
    
    int findLast(int[] nums, int target) {
        int index = -1;
        int start = 0;
        int end = nums.length - 1;
        while (start <= end) {
            int mid = start + (end - start) / 2;
            if (nums[mid] <= target) start = mid + 1;
            else end = mid - 1;
            
            if (nums[mid] == target) index = mid;
        }
        return index;
    }
}


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