LEETCODE PROBLEM -- 1|| TWO SUM by using JAVA ||TAMIL|| #leetcode #placement смотреть онлайн

Certainly! Here's a detailed explanation of the "Two Sum" problem on LeetCode.

Problem Statement:
Given an array of integers `nums` and a target integer `target`, you need to find two numbers such that they add up to the `target`. You are required to return the indices of these two numbers.

Assumptions:
- Each input would have exactly one solution.
- You may not use the same element twice.

To solve this problem efficiently, we can utilize a hash table (dictionary) to store the previously seen elements as we traverse the array.

Here's the step-by-step approach:

1. Create an empty hash table to store the elements and their indices.

2. Iterate through the array `nums` using a loop.

3. For each element `num` at index `i`, calculate the `complement` by subtracting `num` from the `target` value. The complement is the value that, when added to `num`, gives the target.

4. Check if the complement exists in the hash table. If it does, we have found the two numbers that add up to the target. Return the indices of `num` (current index) and its complement (stored index) as an array.

5. If the complement does not exist in the hash table, add `num` to the hash table along with its index `i`.

6. If no solution is found after iterating through the entire array, return an empty array or indicate that there is no solution.

This approach ensures that we can quickly look up the complement value for each element while traversing the array, allowing us to find the solution in linear time complexity.

Let's take an example to illustrate the process. Consider the input `nums = [2, 7, 11, 15]` and `target = 9`:

1. Initialize an empty hash table: `num_dict = {}`.

2. Iterating through the array:
- For `num = 2`, the complement is `9 - 2 = 7`. Since `7` is not present in the hash table, we add `num` to the hash table with its index: `num_dict = {2: 0}`.
- For `num = 7`, the complement is `9 - 7 = 2`. Now, `2` is present in the hash table with index `0`, indicating that we have found the solution. We return `[0, 1]` as the result.

The solution effectively finds the indices of the two numbers that add up to the target value by utilizing a hash table to store the previously encountered elements.

The time complexity of this solution is O(n) since we iterate through the array only once. The space complexity is also O(n) because, in the worst case, we may need to store all the elements of the array in the hash table.