Find Target Indices After Sorting Array - Complete Solution Guide

Find Target Indices After Sorting Array is LeetCode problem 2089, a Easy level challenge. This complete guide provides step-by-step explanations, multiple solution approaches, and optimized code in python3, java, cpp, c.

Problem Statement

You are given a 0-indexed integer array nums and a target element target . A target index is an index i such that nums[i] == target . Return a list of the target indices of nums after sorting nums in non-decreasing order . If there are no target indices, return an empty list . The returned list must be sorted in increasing order. Example 1: Input: nums = [1,2,5,2,3], target = 2 Output: [1,2] Explanation: After sorting, nums is [1, 2 , 2 ,3,5]. The indices where nums[i] == 2 are 1 and 2. Example

Detailed Explanation

The problem asks you to find all indices of a given `target` element within an integer array `nums` after sorting `nums` in non-decreasing order. The input is a 0-indexed integer array `nums` and an integer `target`. The output is a list of indices (also 0-indexed) where the `target` value appears in the sorted `nums` array. If the `target` is not found, an empty list is returned. The output list must be sorted in increasing order.

Solution Approach

The provided solutions all follow a straightforward approach. First, they sort the input array `nums` in non-decreasing order. Then, they iterate through the sorted array and check if each element is equal to the `target`. If it is, the index is added to the result list. Finally, the sorted result list of indices is returned.

Step-by-Step Algorithm

1. Sort the input array `nums` using a suitable sorting algorithm (e.g., built-in sort functions like `Arrays.sort()` in Java or `sort()` in Python and C++).
2. Iterate through the sorted array `nums`.
3. For each element `nums[i]`, check if it is equal to the `target`.
4. If `nums[i]` equals `target`, add the index `i` to the `result` list.
5. Return the `result` list.

Key Insights

• The problem requires sorting the input array first to easily identify target indices.
• A linear scan after sorting is sufficient to find all occurrences of the target and their indices.
• Efficient sorting algorithms (like merge sort or quicksort) are crucial for optimal time complexity.

Complexity Analysis

Time Complexity: O(n log n)

Space Complexity: O(n)

Topics

This problem involves: Array, Binary Search, Sorting.

Companies

Asked at: TikTok.