Given an array of integers for each element determine whether that element occurs earlier

General
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given an array of integers for each element determine whether that element occurs earlier

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How to Determine if an Element Occurs Earlier in an Array

Answer: To determine whether each element in an array of integers has occurred earlier, you can follow these steps:

  1. Initialize a Set for Tracking: Use a set to keep track of the elements you have already seen as you iterate through the array.

  2. Iterate Through the Array: Loop through each element in the array.

  3. Check If the Element Is in the Set:

    • If the element is in the set, it means it has appeared before.
    • If the element is not in the set, it is the first time you are encountering this element.

  4. Update the Set: Add the current element to the set if it’s not already there.

Here is some example code in Python to illustrate these steps:

def check_elements(arr):
    seen_elements = set()
    result = []
    
    for elem in arr:
        if elem in seen_elements:
            result.append(True)  # This element has occurred earlier
        else:
            result.append(False)  # This is the first occurrence of the element
            seen_elements.add(elem)
    
    return result

# Example usage
array = [3, 5, 3, 2, 6, 5]
print(check_elements(array))  # Output: [False, False, True, False, False, True]

Explanation:

  • The seen_elements set keeps track of all elements encountered so far.
  • As you iterate through array, check if elem is in seen_elements.
  • Append True to result if elem is found in the set, indicating it has appeared earlier; otherwise, append False.

Summary: This approach efficiently determines whether each element in an array appears earlier by utilizing a set to track previously seen elements, ensuring each lookup and insertion is done in constant average time.