2 Sum Solution

Solution.java

public class Solution {
    public int[] twoSum(int[] nums, int target) {
        int[] indexes = new int[]{-1, -1};
        Map<Integer, List<Integer>> contents = new HashMap<>();
        
        /*
        Let's record where we find a value in the map. 
        This safe guards if a value appears twice.
        */
        for(int i = 0; i < nums.length; i++) {
            int key = nums[i];
            
            /* 
            Check if we already are holding this key, 
            if we are not, add it and store where it is. 
            Otherwise, append the location.
            */
            if(contents.containsKey(key)) {
                contents.get(key).add(i);
            } else {
                List<Integer> indexesFound = new ArrayList<>(2);
                indexesFound.add(i);
                contents.put(key, indexesFound);
            }
        }
        
        //Now, let's do our search.
        for(int i = 0; i < nums.length; i++) {
            int valueA = nums[i];
            int valueWanted = target - valueA;
            
            //If we find the value we wanted, we're almost done!
            boolean found = contents.containsKey(valueWanted);
            if (found) {
                /*
                If it happens to be the same as valueA, 
                make sure we have more than 1 to work with.
                */
                if (valueA == valueWanted && contents.get(valueWanted).size() > 1) {
                    indexes[0] = i;
                    indexes[1] = contents.get(valueWanted).get(1);
                    return indexes;
                } else if (valueA != valueWanted) {
                    indexes[0] = i;
                    indexes[1] = contents.get(valueWanted).get(0);
                    return indexes;
                }
            }
        }
        
        return indexes;
    }
}