[LeetCode] 1. Two Sum

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].

Thought process:
Iterate through the array. Use a hashmap to keep track of array elements and their corresponding indices. As I come to nums[i], if the hashmap contains target - nums[i], that means we have found the pair.

Solution:

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class Solution {
    public int[] twoSum(int[] nums, int target) {
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            if (map.containsKey(target - nums[i])) {
                return new int[]{ map.get(target - nums[i]), i };
            }
            map.put(nums[i], i);
        }
        return new int[]{ -1, -1 };
    }
}

Time complexity: O(n).
Location: Philadelphia, PA, USA

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