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@alexradzin
Last active June 12, 2022 13:51
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Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
package com.alexr.exercise;
import org.junit.jupiter.api.Test;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.stream.Stream;
import static java.util.stream.Collectors.toList;
import static org.junit.jupiter.api.Assertions.assertArrayEquals;
import static org.junit.jupiter.api.Assertions.assertNull;
/**
* Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
*
* You may assume that each input would have exactly one solution, and you may not use the same element twice.
*
* You can return the answer in any order.
* Example 1
* Input: nums = [2,7,11,15], target = 9
* Output: [0,1]
* Output: Because nums[0] + nums[1] == 9, we return [0, 1].
* Example 2
* Input: nums = [3,2,4], target = 6
* Output: [1,2]
* Example 3
* Input: nums = [3,3], target = 6
* Output: [0,1]
*/
public class TaskTest {
public static int[] findSumEqualToTarget(int[] arr, int target) {
Map<Integer, List<Integer>> map = new HashMap<>();
for (int i = 0; i < arr.length; i++) {
map.merge(arr[i], List.of(i), (existing, addition) -> Stream.of(existing, addition).flatMap(Collection::stream).collect(toList()));
}
for (Map.Entry<Integer, List<Integer>> e : map.entrySet()) {
int value = e.getKey();
int pair = target - value;
List<Integer> indexes2 = map.getOrDefault(pair, List.of());
int index1 = e.getValue().get(0);
int nIndexes = indexes2.size();
Integer index2;
if (nIndexes == 1) {
index2 = indexes2.get(0);
return new int[] {index1, index2};
} else if (nIndexes > 1) {
Optional<Integer> i2Opt = indexes2.stream().filter(i -> i != index1).findFirst();
if (i2Opt.isPresent()) {
return new int[] {index1, i2Opt.get()};
}
}
}
return null;
}
@Test
void empty() {
assertNull(findSumEqualToTarget(new int[0], 5));
}
@Test
void one() {
assertNull(findSumEqualToTarget(new int[] {5}, 5));
}
@Test
void twoMatching() {
assertArrayEquals(new int[] {0, 1}, findSumEqualToTarget(new int[] {2,3}, 5));
}
@Test
void twoNotMatching() {
assertNull(findSumEqualToTarget(new int[]{2, 3}, 7));
}
@Test
void example1() {
assertArrayEquals(new int[]{0, 1}, findSumEqualToTarget(new int[]{2, 7, 11, 15}, 9));
}
@Test
void example2() {
assertArrayEquals(new int[]{1, 2}, findSumEqualToTarget(new int[]{3,2,4}, 6));
}
@Test
void example3() {
assertArrayEquals(new int[]{0, 1}, findSumEqualToTarget(new int[]{3,3}, 6));
}
}
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