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Permutations.swift
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Permutations.swift
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/**
* Question Link: https://leetcode.com/problems/permutations/
* Primary idea: Classic Depth-first Search, remember backtracking
*
* Time Complexity: O(n!), Space Complexity: O(n)
*
*/
class Permutations {
func permute(_ nums: [Int]) -> [[Int]] {
var res = [[Int]]()
var path = [Int]()
var isVisited = [Bool](repeating: false, count: nums.count)
dfs(&res, &path, &isVisited, nums)
return res
}
private func dfs(_ res: inout [[Int]], _ path: inout [Int], _ isVisited: inout [Bool], _ nums: [Int]) {
guard path.count != nums.count else {
res.append(path)
return
}
for (i, num) in nums.enumerated() where !isVisited[i] {
path.append(num)
isVisited[i] = true
dfs(&res, &path, &isVisited, nums)
isVisited[i] = false
path.removeLast()
}
}
}