Python: Find the indices of two numbers that sum to 0 in a given list

Python Programming Puzzles: Exercise-29 with Solution

Write a Python program to find the indices of two numbers that sum to 0 in a given list of numbers.

Input:
[1, -4, 6, 7, 4]
Output:
[4, 1]

Input:
[1232, -20352, 12547, 12440, 741, 341, 525, 20352, 91, 20]
Output:
[1, 7]

Pictorial Presentation:

Sample Solution-1:

Python Code:

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

def test(nums):
    s = set(nums)
    for i in s:
        if -i in s:
            return [nums.index(i), nums.index(-i)]

nums = [1, -4, 6, 7, 4]
print("Original List:")
print(nums) 
print("Indices of two numbers that sum to 0 in the said list:")
print(test(nums))
nums=[1232, -20352, 12547, 12440, 741, 341, 525, 20352, 91, 20]
print("\nOriginal List:")
print(nums) 
print("Indices of two numbers that sum to 0 in the said list:")
print(test(nums)) 

Sample Output:

Original List:
[1, -4, 6, 7, 4]
Indices of two numbers that sum to 0 in the said list:
[4, 1]

Original List:
[1232, -20352, 12547, 12440, 741, 341, 525, 20352, 91, 20]
Indices of two numbers that sum to 0 in the said list:
[1, 7]

Flowchart:

Visualize Python code execution:

The following tool visualize what the computer is doing step-by-step as it executes the said program:

Sample Solution-2:

Python Code:

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

def test(nums):
    result = []
    # For each index in the list:
    for ind in range(len(nums)):
        # For each index in the list:
        for i in range(len(nums)):
            # If the number at the current index and the other index sum to zero
            if ind != i and nums[ind] + nums[i] == 0:
                result.append(ind)
                result.append(i)
                # Found the indices; no need to go through the whole list
                return result

nums = [1, -4, 6, 7, 4]
print("Original List:")
print(nums) 
print("Indices of two numbers that sum to 0 in the said list:")
print(test(nums))
nums=[1232, -20352, 12547, 12440, 741, 341, 525, 20352, 91, 20]
print("\nOriginal List:")
print(nums) 
print("Indices of two numbers that sum to 0 in the said list:")
print(test(nums)) 

Sample Output:

Original List:
[1, -4, 6, 7, 4]
Indices of two numbers that sum to 0 in the said list:
[1, 4]

Original List:
[1232, -20352, 12547, 12440, 741, 341, 525, 20352, 91, 20]
Indices of two numbers that sum to 0 in the said list:
[1, 7]

Flowchart:

Visualize Python code execution:

The following tool visualize what the computer is doing step-by-step as it executes the said program:

Python Code Editor :

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