LeetCode 2007: Find Original Array From Doubled Array Solution
Master LeetCode problem 2007 (Find Original Array From Doubled Array), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.
2007. Find Original Array From Doubled Array
Problem Explanation
Explanation:
To solve this problem, we can iterate over the changed array and build a frequency map of each element. Then, for each element x in the frequency map, we check if the frequency of 2*x is greater than or equal to the frequency of x. If this condition is satisfied, we decrement the frequency of 2*x by the frequency of x and continue to the next element. If at any point the condition is not met, we return an empty array.
Time Complexity:
The time complexity of this solution is O(n), where n is the number of elements in the changed array.
Space Complexity:
The space complexity of this solution is O(n), where n is the number of elements in the changed array.
Solution Code
import java.util.*;
class Solution {
public int[] findOriginalArray(int[] changed) {
if (changed.length % 2 != 0) {
return new int[0];
}
Map<Integer, Integer> freqMap = new HashMap<>();
for (int num : changed) {
freqMap.put(num, freqMap.getOrDefault(num, 0) + 1);
}
List<Integer> result = new ArrayList<>();
for (int num : changed) {
if (freqMap.get(num) == 0) {
continue;
}
if (freqMap.getOrDefault(2 * num, 0) < freqMap.get(num)) {
return new int[0];
}
result.add(num);
freqMap.put(num, freqMap.get(num) - 1);
freqMap.put(2 * num, freqMap.get(2 * num) - 1);
}
return result.stream().mapToInt(Integer::intValue).toArray();
}
}Try It Yourself
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