TwoSum.java

# METHOD 1 : using map

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

# METHOD 2 : using 2 for loops

class Solution {
    public int[] twoSum(int[] nums, int target) {
        int size = nums.length;
        int[] ans = new int[2];
        for (int i = 0; i < size - 1; i++) {
            for (int j = i + 1; j < size; j++) {
                if (nums[i] + nums[j] == target) {
                    ans[0] = i;
                    ans[1] = j;
                    return ans;
                }
            }
        }
        return ans;
    }
}