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: The solution set must not contain duplicate quadruplets.
For example, given array
S = [1, 0, -1, 0, -2, 2]
and
target = 0
A solution set is:
[ [-1, 0, 0, 1], [-2, -1, 1, 2], [-2, 0, 0, 2] ]
import scala.util.Sorting.quickSort
def fourSum(nums: Array[Int], target: Int):List[(Int,Int,Int,Int)] = {
quickSort(nums)
var ret:List[(Int,Int,Int,Int)] = Nil
for (i <- 0 until nums.length) {
for (j <- i + 1 until nums.length) {
// fixed first two indexes
var (k,l) = (j + 1, nums.length - 1)
while (k < l) {
nums(i)+nums(j)+nums(k)+nums(l) match {
case sum if sum == target => {
val tup = (nums(i),nums(j),nums(k),nums(l))
// check duplicate
if (ret.isEmpty || tup != ret.head) {
ret = tup :: ret
}
l -= 1
k += 1
}
case sum if sum > target => l -= 1
case sum if sum < target => k += 1
}
}
}
}
ret
}
fourSum(Array(1, 0, -1, -1, 0, -2, 2), 0)
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