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Find Unique Triplets with Target Sum

Certification: Intermediate Level Accuracy: 0% Submissions: 0 Points: 8

Write a C# function to find all unique triplets in an array that sum to a specified target value. A triplet is a set of three integers. The solution should avoid duplicate triplets in the output.

Example 1
    

  • Input: nums = [-1, 0, 1, 2, -1, -4], target = 0
    • 

  • Output: [[-1, -1, 2], [-1, 0, 1]]
    • 

  • Explanation: 
      
   
    • Step 1: Sort the input array (for efficient processing): [-4, -1, -1, 0, 1, 2].
      • 
   
    • Step 2: Iterate through the array, fixing the first element of potential triplets.
      • 
   
    • Step 3: For each fixed element, use two pointers technique to find pairs that complete the triplet.
      • 
   
    • Step 4: When a triplet is found (nums[0] + nums[4] + nums[2] = -1 + (-1) + 2 = 0), add it to results.
      • 
   
    • Step 5: Skip duplicate elements to avoid duplicate triplets.
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    • Step 6: Repeat until all unique triplets are found ([-1, -1, 2], [-1, 0, 1]).
      • 

    •
Example 2
    

  • Input: nums = [1, 2, 3, 4, 5], target = 12
    • 

  • Output: [[3, 4, 5]]
    • 

  • Explanation: 
      
   
    • Step 1: Sort the input array (already sorted): [1, 2, 3, 4, 5].
      • 
   
    • Step 2: Iterate through the array, fixing the first element of potential triplets.
      • 
   
    • Step 3: For each fixed element, use two pointers technique to find pairs that complete the triplet.
      • 
   
    • Step 4: When a triplet is found (nums[2] + nums[3] + nums[4] = 3 + 4 + 5 = 12), add it to results.
      • 
   
    • Step 5: No other triplets sum to 12, so return [[3, 4, 5]].
      • 

    •
Constraints
    

  • 3 ≤ nums.length ≤ 3000
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  • -10^5 ≤ nums[i] ≤ 10^5
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  • -10^5 ≤ target ≤ 10^5
    • 

  • Time Complexity: O(n²) where n is the length of the array
    • 

  • Space Complexity: O(n) for storing the results
    •
ArraysControl StructuresKPMGPhillips
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Hint
Solution

Solution Hints

    
  
  • Sort the array to avoid duplicate triplets
    • 
  
  • Use a two-pointer approach for each element
    • 
  
  • Fix one element and find the other two using the two-pointer technique
    • 
  
  • Skip duplicate elements to avoid duplicate triplets
    • 
  
  • Use a set or list to store unique triplets
    •

Steps to solve by this approach:

 Step 1: Sort the array to facilitate the two-pointer approach and handle duplicates.
 Step 2: Iterate through the array, fixing one element at a time.
 Step 3: For each fixed element, use two pointers (left and right) to find pairs that sum with the fixed element to the target.
 Step 4: When a valid triplet is found, add it to the result and skip duplicate elements.
 Step 5: Continue the process until all possible triplets are found.


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