package gliderai;
import java.util.HashMap;
import java.util.Objects;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
public class TwoSum {
public int[] twoSum(int[] nums, int target) {
// Java 17 feature: var for Type Inference
if (nums == null || nums.length < 2) {
throw new IllegalArgumentException("Input array must have at least two elements.");
}
var map = new HashMap();
for (int i = 0; i < nums.length; i++) {
int complement = target - nums[i];
if (map.containsKey(complement)) {
return new int[] { map.get(complement), i };
}
map.put(nums[i], i);
}
throw new IllegalArgumentException("No solution found: No two numbers sum up to the target.");
}
//Before Java 17
public int[] twoSumSol(int[] nums, int target) {
//Before Java 17
HashMap map = new HashMap<>();
for (int i = 0; i < nums.length; i++) {
int complement = target - nums[i];
// Check if complement exists in the map
if (map.containsKey(complement)) {
return new int[]{map.get(complement), i};
}
// Store the current number with its index
map.put(nums[i], i);
}
return new int[]{}; // Should never reach here as per problem constraints
}
// find all valid pairs in the array
public int[] twoSumStreamSol(int[] nums, int target) {
// find all valid pairs in the array
var map1 = new HashMap();
// add return to Line 61
IntStream.range(0, nums.length)
.mapToObj(i -> {
int complement = target - nums[i];
if (map1.containsKey(complement)) {
return new int[]{map1.get(complement), i};
}
map1.put(nums[i], i);
return null;
})
.filter(Objects::nonNull) // Remove null values
.collect(Collectors.toList()); // Collect all valid pairs
// Java 8 and later --> Find only one pair in the array
if (nums == null || nums.length < 2) {
throw new IllegalArgumentException("Input array must have at least two elements.");
}
var map = new HashMap();
return IntStream.range(0, nums.length)
.mapToObj(i -> {
int complement = target - nums[i];
if (map.containsKey(complement)) {
return new int[]{map.get(complement), i};
}
map.put(nums[i], i);
return null;
})
.filter(result -> result != null) // Filter out null results
.findFirst() // Get the first valid result
.orElseThrow(() -> new IllegalArgumentException("No solution found: No two numbers sum up to the target."));
}
public static void main(String[] args) {
TwoSum solution = new TwoSum();
try {
int[] nums = { 2, 7, 11, 15 };
int target = 9;
int[] result = solution.twoSum(nums, target);
System.out.println("Indices: [" + result[0] + ", " + result[1] + "]");
} catch (IllegalArgumentException e) {
System.err.println("Error: " + e.getMessage());
}
}
}
/* New Features Used from Java 17
1. var for Type Inference – Reduces verbosity (used for HashMap).
2. Enhanced Exception Handling – Uses IllegalArgumentException with meaningful messages.
3. Improved Readability & Robustness.
Edge Case How It’s Handled
Null Array (null) Throws IllegalArgumentException
Array with Less than 2 Elements ([1]) Throws IllegalArgumentException
No Valid Pair Exists ([1, 2, 3], target=10) Throws IllegalArgumentException
Negative Numbers ([-1, -2, -3, -4]) Works correctly
Zeros and Duplicates ([0, 0, 3, 4], target=0) Works correctly
Large Input Size (10^6 elements) Runs in O(n) and performs well
*/
// Time Complexity: O(n)
// Space Complexity: O(n)