Python Bisect: Find three integers which gives the sum of zero in a given array of integers using Binary Search

Last update on April 01 2025 13:14:26 (UTC/GMT +8 hours)

7. Triplet Sum Zero (Using Bisect)

Write a Python program to find three integers which give the sum of zero in a given array of integers using Binary Search (bisect).

Sample Solution:

Python Code:

from bisect import bisect, bisect_left
from collections import Counter
class Solution:
    def three_Sum(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        triplets = []
        if len(nums) < 3:
            return triplets
        num_freq = Counter(nums)
        nums = sorted(num_freq)  # Sorted unique numbers
        max_num = nums[-1]
        for i, v in enumerate(nums):
            if num_freq[v] >= 2:
                complement =  -2 * v
                if complement in num_freq:
                    if complement != v or num_freq[v] >= 3:
                        triplets.append([v] * 2 + [complement])

            # When all 3 numbers are different.
            if v < 0:  # Only when v is the smallest
                two_sum = -v

                # Lower/upper bound of the smaller of remainingtwo.
                lb = bisect_left(nums, two_sum - max_num, i + 1)
                ub = bisect(nums, two_sum // 2, lb)                       
                for u in nums[lb : ub]:
                    complement = two_sum - u
                    if complement in num_freq and u != complement:
                        triplets.append([v, u, complement])
        return triplets
nums = [-20, 0, 20, 40, -20, -40, 80]
s = Solution()
result = s.three_Sum(nums)
print(result)
nums = [1, 2, 3, 4, 5, -6]
result = s.three_Sum(nums)
print(result)

Sample Output:

[[-40, 0, 40], [-20, -20, 40], [-20, 0, 20]]
[[-6, 1, 5], [-6, 2, 4]]

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Python program to find all unique triplets in a sorted array that sum to zero using bisect to locate complement values.
• Write a Python script to implement a function that finds zero-sum triplets in a sorted list and then prints each triplet, ensuring no duplicates.
• Write a Python program to search for three numbers in a sorted array that add up to zero using a combination of binary search and two-pointer technique.
• Write a Python function to output all sets of three numbers from a sorted list whose sum is zero, using bisect to optimize the inner search loop.

Python Code Editor:

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