[Swift] 4Sum

Given an array nums of n integers, return an array of all the unique quadruplets [nums[a], nums[b], nums[c], nums[d]] such that:

• 0 <= a, b, c, d < n
• a, b, c, and d are distinct.
• nums[a] + nums[b] + nums[c] + nums[d] == target

You may return the answer in any order.

Example 1:

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

Example 2:

Input: nums = [2,2,2,2,2], target = 8
Output: [[2,2,2,2]]

Constraints:

• 1 <= nums.length <= 200
• $-10^9$ <= nums[i] <= $10^9$
• $-10^9$ <= target <= $10^9$

풀러가기

문제 이해

코드

func fourSum(_ nums: [Int], _ target: Int) -> [[Int]] {
  if nums.count < 4 {
    return []
  }
  
  var ret: Set<[Int]> = []
  var nums = nums.sorted()
  
  for a in 0 ..< nums.count - 3 {
    for b in a + 1 ..< nums.count - 2 {
      var c = b + 1
      var d = nums.count - 1
      
      while c < d {
        let sum = nums[a] + nums[b] + nums[c] + nums[d]
        if sum == target {
          ret.insert([nums[a], nums[b], nums[c], nums[d]])
        }
        
        if sum < target {
          c += 1
        } else {
          d -= 1
        }
      }
    }
  }
  
  return ret.map { Array($0) }
}

풀이

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