Given the array [1,2,3,4,2,5,1], output [2,1]. Write the code to find elements that appear more than once.

Question

Assisting AI · Accepted Answer

Use a hash map (dictionary) to count occurrences of each element. Iterate through the array, incrementing the count for each value. After counting, iterate through the map and collect keys whose count is greater than one. This yields the list of duplicates. Complexity is O(n) time and O(n) space. Example in Python:

```python
arr = [1,2,3,4,2,5,1]
counts = {}
for num in arr:
    counts[num] = counts.get(num, 0) + 1
result = [num for num, cnt in counts.items() if cnt > 1]
print(result)  # [1, 2]
```

Given the array [1,2,3,4,2,5,1], output [2,1]. Write the code to find elements that appear more than once.

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