Two Sum LeetCode Interview Question (Explained Simply)

Given an array of integers and a target value, return the indices of 2 numbers that add up to the input target value.

The first “two sum” in our example is 8 and 2, because they add up to 10.

LeetCode also asks us to return the indices which are [0, 2]

• There cannot be multiple solutions and only one solution will be found.
• You will also be guaranteed a solution.
• Only distinct numbers will be accepted ([2,2] are not valid pairs.

Hash Map Solution

The most common solution would be to declare two pointers and search for pairs that equal the target.

• First, initialize a pointer at the first position. Start a loop with p1 as our loop’s index from 0 till end of array.
• The second value we are searching for must be equal to the target minus the first pointer
• Search each remaining value for the target minus the first pointer
• Lastly, most first pointer and repeat.

twoSum(numbers, target) {
    let indices = {};
    for(i=0;i<numbers.length;i++){
        var num = target - numbers[i]
        if(indices[num] !== undefined) {
            return [indices[num], i]
        }
        indices[numbers[i]] = i;
    }
}