Python: Find the first duplicate element in a given array of integers

Last update on May 28 2022 13:31:29 (UTC/GMT +8 hours)

Python: Array Exercise-15 with Solution

Write a Python program to find the first duplicate element in a given array of integers. Return -1 If there are no such elements.

Sample Solution:

Python Code :

def find_first_duplicate(nums):
    num_set = set()
    no_duplicate = -1

    for i in range(len(nums)):

        if nums[i] in num_set:
            return nums[i]
        else:
            num_set.add(nums[i])

    return no_duplicate

print(find_first_duplicate([1, 2, 3, 4, 4, 5]))
print(find_first_duplicate([1, 2, 3, 4]))
print(find_first_duplicate([1, 1, 2, 3, 3, 2, 2]))

Sample Output:

4
-1
1

Python Code Editor:

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Previous: Write a Python program to find if a given array of integers contains any duplicate element. Return true if any value appears at least twice in the said array and return false if every element is distinct.
Next: Write a Python program to check whether it follows the sequence given in the patterns array.

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Python: Tips of the Day

Find current directory and file's directory:

To get the full path to the directory a Python file is contained in, write this in that file:

import os 
dir_path = os.path.dirname(os.path.realpath(__file__))

(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)

To get the current working directory use

import os
cwd = os.getcwd()

Documentation references for the modules, constants and functions used above:

The os and os.path modules.
The __file__ constant
os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")
os.path.dirname(path) (returns "the directory name of pathname path")
os.getcwd() (returns "a string representing the current working directory")
os.chdir(path) ("change the current working directory to path")

Ref: https://bit.ly/3fy0R6m