4 Sum

Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.

Note:

  • Elements in a quadruplet (a,b,c,d) must be in non-descending order. (ie, a ≤ b ≤ c ≤ d)
  • The solution set must not contain duplicate quadruplets.

Example :
Given array S = {1 0 -1 0 -2 2}, and target = 0
A solution set is:

    (-2, -1, 1, 2)
    (-2,  0, 0, 2)
    (-1,  0, 0, 1)

Also make sure that the solution set is lexicographically sorted.
Solution[i] < Solution[j] iff Solution[i][0] < Solution[j][0] OR (Solution[i][0] == Solution[j][0] AND ... Solution[i][k] < Solution[j][k])

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