Two Sum - LeetCode Solution

Two Sum - LeetCode Solution

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].

Java Solution:

Approach : Two Pass Hash Table

class Solution {
    public int[] twoSum(int[] nums, int target) {
        Map<Integer,Integer> map = new HashMap<>();
        for(int i =0 ;i < nums.length;i++){
            map.put(nums[i],i);
        }
        for(int i =0; i< nums.length;i++){
            int element = target-nums[i];
            if(map.containsKey(element) && map.get(element)!=i)
                return new int[]{i,map.get(element)};
        }
        throw new IllegalArgumentException("No two sum solution");

         }
}

Time Complexity : O(n) HashTable reduces lookup time to O(1).

Space Complexity : O(n) This space is used by hashtable to store the number of elements n.