[Swift]LeetCode47. 全排列 II | Permutations II

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Given a collection of numbers that might contain duplicates, return all possible unique permutations.

Example:

Input: [1,1,2]
Output:
[
  [1,1,2],
  [1,2,1],
  [2,1,1]
]

---

给定一个可包含重复数字的序列，返回所有不重复的全排列。

示例:

输入: [1,1,2]
输出:
[
  [1,1,2],
  [1,2,1],
  [2,1,1]
]

---

20ms

class Solution {
    func permuteUnique(_ nums: [Int]) -> [[Int]] {
        var ans = [[Int]]()
        var nums = nums
        permuteUnique(&nums, 0, &ans)
        return ans
    }
    
    func permuteUnique(_ nums: inout [Int], _ startIndex: Int, _ ans: inout [[Int]]) {
        if startIndex >= nums.count {
            ans.append(nums)
        }
        
        var visited = Set<Int>()
        for index in startIndex..<nums.count {
            if visited.insert(nums[index]).inserted {
                nums.swapAt(startIndex, index)
                permuteUnique(&nums, startIndex+1, &ans)
                nums.swapAt(startIndex, index)    
            }
        }
    }
}

---

24ms

class Solution {
    func permuteUnique(_ nums: [Int]) -> [[Int]] {
        let sortedNums = nums.sorted()
        
        var temp = [Int]()
        var result = [[Int]]()
        var isvisited = Array(repeating: false, count: nums.count)
        
        backTracking(sortedNums, &result, &temp, &isvisited)
        return result 
    }
    
    func backTracking(_ nums: [Int], _ result: inout [[Int]], _ temp: inout [Int], _ isvisited: inout [Bool]) {
        if temp.count == nums.count {
            result.append(temp)
            return
        }
        
        for i in 0 ..< nums.count where !isvisited[i] {
            if i > 0 && nums[i] == nums[i - 1] && !isvisited[i - 1]{  
                continue
            }
            temp.append(nums[i])
            isvisited[i] = true
            backTracking(nums, &result, &temp, &isvisited)
            isvisited[i] = false
            temp.removeLast()
        }
        
        
    }
}

---

44ms

class Solution {
    private func backtrack(_ nums: [Int], _ begin: Int,  results: inout [[Int]]) {
        if begin == nums.count - 1 {
            results.append(nums)
            return
        }

        var nums = nums

        for i in begin..<nums.count {
            if i == begin || nums[i] != nums[begin]  {
                nums.swapAt(begin, i)
                backtrack(nums, begin + 1, results: &results)
            }
        }
    }
    
    func permuteUnique(_ nums: [Int]) -> [[Int]] {
        var results = [[Int]]()
        var nums = nums.sorted()
        backtrack(nums, 0, results: &results)
        return results
    }
}

---

56ms

class Solution {
    func permuteUnique(_ nums: [Int]) -> [[Int]] {
        var res = [[Int]]()
        var index = 0
        var nums = nums
        helper(&res, index, &nums)
        return res
    }
    
    
    private func helper(_ res: inout [[Int]], _ index: Int, _ nums: inout [Int]) {
        if index == nums.count {
            res.append(nums)
            return
        }
        
        var usedSet = Set<Int>()
        for i in index..<nums.count {
            if usedSet.contains(nums[i]) {
                continue
            }
            
            usedSet.insert(nums[i])
            nums.swapAt(index, i)
            helper(&res, index + 1, &nums)
            nums.swapAt(index, i)
        }
    }
}

---

60ms

class Solution {
    var result = [[Int]]()
    func permuteUnique(_ nums: [Int]) -> [[Int]] {
        var nums = nums
        permute(&nums)
      return result
    }
    func permute(_ nums: inout [Int], _ index: Int = 0) {
      if index == nums.count{
            result.append(nums) 
          return
      }
        for i in index..<nums.count{
            if shouldSwap(nums, index, i){
                nums.swapAt(index, i)
                permute(&nums, index+1)
                nums.swapAt(index, i) 
            }
        }
    }    
    
    func shouldSwap(_ nums:[Int],_ start: Int,_ current: Int) -> Bool{
        for i in start..<current{
            if nums[i] == nums[current]{
                return false
            }
        }
        return true
    }
}

---

76ms

class Solution {
    func permuteUnique(_ nums: [Int]) -> [[Int]] {

        var res = [[Int]]()
        var path = [Int]()
        let nums = nums.sorted()
        var isVisited = [Bool](repeating:false,count:nums.count)
        dfs(&res,&path,&isVisited,nums)
        return res
    }

    func dfs(_ res:inout [[Int]],_ path:inout [Int],_ isVisited:inout [Bool],_ nums:[Int]) {
        if path.count == nums.count {
            res.append(path)
            return
        }

        for (i,num) in nums.enumerated() {
            if isVisited[i] || (i > 0 && nums[i] == nums[i-1] && !isVisited[i-1]) {
                continue
            }

                path.append(num)
                isVisited[i] = true
                dfs(&res,&path,&isVisited,nums)
                isVisited[i] = false
                path.removeLast()

        }
    }

    func toString(_ array:[Int]) -> String {
        var str = ""
        for (i,num) in array.enumerated() {
            str = str + "\(num)"
        }

        return str
    }
}