LeetCode Programming (#1 Two Sum)

This is my second posting for solving one of the LeetCode programming problem called Two Sum.

Two Sum - LeetCode

The problem is simple: “Given an array of integers, return indices of the two numbers such that they add up to a specific target. You may assume that each input would have exactly one solution, and you may not use the same element twice.”

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

Idea

• We need to have a data structure that contains {Number -> index}
• If there exists such two numbers where num1 + num2 = target, then we would also have num2 = target — num1

Pseudocode

class Solution {
    public int[] twoSum(int[] nums, int target) {
        // 1. initialize HashMap for {Number -> Index}
        // 2. iterate the array
        // 3. check if such 'num2' exists in the hashmap
            
        // 4. if not exist, add new pair to the hashmap
    }
}

Code

Note that you can return the result as return new int[]{i, map.get(nums2)

Very straightforward question using HashMap. Thanks for reading!