Python: Find the indices of the closest pair from given a list of numbers

Last update on May 30 2025 11:49:01 (UTC/GMT +8 hours)

Indices of Closest Pair

Write a Python program to find the indices of the closest pair from a list of numbers.

Input: [1, 7, 9, 2, 10]
Output:
[0, 3]

Input: [1.1, 4.25, 0.79, 1.0, 4.23]
Output:
[4, 1]

Input: [0.21, 11.3, 2.01, 8.0, 10.0, 3.0, 15.2]
Output:
[2, 5]

Visual Presentation:

Sample Solution:

Python Code:

# License: https://bit.ly/3oLErEI

def test(nums):
    # Initialize variables to store indices of the closest pair and the closest distance
    closest_inds = None
    closest_dist = None
    
    # Iterate through each element in the list
    for ind, num in enumerate(nums):
        # Compare each element with every other element in the list
        for other_ind, num2 in enumerate(nums):
            # Check if the elements are distinct and calculate the absolute difference
            if num != num2 and ((closest_dist is None) or abs(num - num2) < closest_dist):
                # Update the closest distance and indices
                closest_dist = abs(num - num2)
                
                # Determine the order of indices based on the magnitude of the numbers
                if num <= num2:
                    closest_inds = [ind, other_ind]
                else:
                    closest_inds = [other_ind, ind]
    
    # Return the indices of the closest pair
    return closest_inds

# Example 1
nums1 = [1, 7, 9, 2, 10]
print("List of numbers:", nums1)
print("Indices of the closest pair from the said list of numbers:")
print(test(nums1))

# Example 2
nums2 = [1.1, 4.25, 0.79, 1.0, 4.23]
print("\nList of numbers:", nums2)
print("Indices of the closest pair from the said list of numbers:")
print(test(nums2))

# Example 3
nums3 = [0.21, 11.3, 2.01, 8.0, 10.0, 3.0, 15.2]
print("\nList of numbers:", nums3)
print("Indices of the closest pair from the said list of numbers:")
print(test(nums3))

Sample Output:

List of numbers: [1, 7, 9, 2, 10]
Indices of the closest pair from the said list of numbers:
[0, 3]

List of numbers: [1.1, 4.25, 0.79, 1.0, 4.23]
Indices of the closest pair from the said list of numbers:
[4, 1]

List of numbers: [0.21, 11.3, 2.01, 8.0, 10.0, 3.0, 15.2]
Indices of the closest pair from the said list of numbers:
[2, 5]

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Python program to find the indices of two distinct numbers in a list that have the smallest absolute difference.
• Write a Python program to iterate over all pairs of numbers in a list and return the indices of the pair with the minimal difference.
• Write a Python program to sort a list and then map back the closest pair’s original indices.
• Write a Python program to implement a two-pointer approach on a sorted list and return the corresponding original indices of the closest pair.

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