leetcode_gym/_problems/threeSum.md

layout, title, last_solved, category, leetcode_url, status

layout	title	last_solved	category	leetcode_url	status
page	Three Sum	2020-07-08	array	https://leetcode.com/problems/3sum	Attempted

Problem

Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Note:

The solution set must not contain duplicate triplets.

Example:

Given array nums = [-1, 0, 1, 2, -1, -4],

A solution set is:
[
  [-1, 0, 1],
  [-1, -1, 2]
]

Solution

---

This triple loop solution will cause duplicates sets.

{% highlight python %}

ans = [] for i in range(len(nums)): for j in range(i, len(nums)): for k in range(j, len(nums)): if nums[i] + nums[j] + nums[k] == 0: ans.append([nums[i], nums[j], nums[k]])

{% endhighlight %}

---

Check out dicussion and timonthy's video

When I tried to mimic that solution on my own:

{% highlight python %}

def threeSum(nums):

nums.sort()
output = []

print(nums)

index = 0
while index<len(nums):

    fixed = nums[index]     # -1
    target = fixed*-1       # want to find 1 in rest of array

    l,r = index+1, len(nums)-1

    while l<r:

        if nums[index] + nums[l] + nums[r] == 0:
            output.append( [nums[index], nums[l], nums[r]] )
        
        l+=1
        r-=1
    

    index+=1

return output

{% endhighlight %}

It will pass the first case:

[-4, -1, -1, 0, 1, 2]
[[-1, -1, 2], [-1, 0, 1]]

But will create a duplicate set on:

[0, 0, 0, 0]
[[0, 0, 0], [0, 0, 0]]

---