# Python: Find the indices of three numbers that sum to 0 in a list

## Python Programming Puzzles: Exercise-72 with Solution

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

Input: [12, -7, 3, -89, 14, 4, -78, -1, 2, 7] Output: [1, 2, 5] Input: [1, 2, 3, 4, 5, 6, -7] Output: [2, 3, 6]

**Pictorial Presentation:**

**Sample Solution:**

**Python Code:**

```
#License: https://bit.ly/3oLErEI
def test(nums):
inv = {n: i for i, n in enumerate(nums)} # note that later duplicates will override earlier entries
for i, n in enumerate(nums):
if inv[n] == i:
del inv[n]
if any((-m - n) in inv for m in nums[:i]): # found solution!
j, m = next((j, m) for j, m in enumerate(nums) if (-m - n) in inv)
k = inv[-m - n]
return sorted([i, j, k])
nums = [12, -7, 3, -89, 14, 4, -78, -1, 2, 7]
print("List of numbers:",nums)
print("Indices of three numbers that sum to 0 in the said list:")
print(test(nums))
nums = [1, 2, 3, 4, 5, 6, -7]
print("\nList of numbers:",nums)
print("Indices of three numbers that sum to 0 in the said list:")
print(test(nums))
```

Sample Output:

List of numbers: [12, -7, 3, -89, 14, 4, -78, -1, 2, 7] Indices of three numbers that sum to 0 in the said list: [1, 2, 5] List of numbers: [1, 2, 3, 4, 5, 6, -7] Indices of three numbers that sum to 0 in the said list: [2, 3, 6]

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