[Swift]LeetCode77. 组合 | Combinations
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➤微信公众号：山青咏芝（shanqingyongzhi）
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➤原文地址：https://www.cnblogs.com/strengthen/p/9933809.html
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Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.
Example:
Input: n = 4, k = 2 Output: [ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4], ]
给定两个整数 n 和 k，返回 1 ... n 中所有可能的 k 个数的组合。
示例:
输入: n = 4, k = 2 输出: [ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4], ]
32ms
1 class Solution { 2 3 func combine(_ n: Int, _ k: Int) -> [[Int]] { 4 guard n > 0 else { 5 return [] 6 } 7 var result : [[Int]] = [] 8 var nums : [Int] = Array(repeating: 0, count: k) 9 combineNext(lastIndex: 1,leftCount: k, numsIndex: 0, result: &result, nums: &nums, maxN: n) 10 return result 11 } 12 private func combineNext(lastIndex:Int,leftCount:Int,numsIndex:Int , result : inout [[Int]] , nums : inout [Int] , maxN : Int) { 13 if leftCount == 0{ 14 result.append(nums) 15 return 16 } 17 if lastIndex>maxN { 18 return 19 } 20 21 for idx in lastIndex...(maxN-leftCount+1) { 22 nums[numsIndex] = idx 23 combineNext(lastIndex: idx+1, leftCount: leftCount-1,numsIndex: numsIndex+1, result: &result, nums: &nums, maxN: maxN) 24 } 25 } 26 }
36ms
1 class Solution { 2 3 func combine(_ n: Int, _ k: Int) -> [[Int]] { 4 guard n > 0 else { 5 return [] 6 } 7 var result = [[Int]]() 8 helper(1, n, k, [Int](), &result) 9 return result 10 } 11 12 func helper(_ start: Int, _ end: Int, _ k: Int, _ added: [Int], _ result: inout [[Int]]) { 13 if k == 0 { 14 result.append(added) 15 return 16 } 17 18 for i in start...(end-k+1) { 19 var tempAdded = added 20 tempAdded.append(i) 21 helper(i+1, end, k-1, tempAdded, &result) 22 } 23 } 24 }
40ms
1 class Solution { 2 func combineHelper(withResult result: inout [[Int]], usingTemp temp: inout [Int], andStart start: Int, andN n: Int, andK k: Int) { 3 4 if (k <= 0) { 5 result.append(temp) 6 return 7 } 8 9 for i in start...n { 10 if (n - i + 1) >= k { 11 temp.append(i) 12 combineHelper(withResult: &result, usingTemp: &temp, andStart: i + 1, andN: n, andK: k - 1) 13 temp.removeLast() 14 } 15 } 16 } 17 18 func combine(_ n: Int, _ k: Int) -> [[Int]] { 19 var result = [[Int]](); 20 var temp = [Int]() 21 combineHelper(withResult: &result, usingTemp: &temp, andStart: 1, andN: n, andK: k) 22 return result 23 } 24 }
48ms
1 class Solution { 2 3 func combine(_ n: Int, _ k: Int) -> [[Int]] { 4 guard n > 0 else { 5 return [] 6 } 7 var result = [[Int]]() 8 helper(1, n, k, [Int](), &result) 9 return result 10 } 11 12 func helper(_ start: Int, _ end: Int, _ k: Int, _ added: [Int], _ result: inout [[Int]]) { 13 if k == 0 { 14 result.append(added) 15 } 16 17 if start > end { 18 return 19 } 20 21 for i in start...(end-k+1) { 22 var tempAdded = added 23 tempAdded.append(i) 24 helper(i+1, end, k-1, tempAdded, &result) 25 } 26 }
68ms
1 class Solution { 2 func combine(_ n: Int, _ k: Int) -> [[Int]] { 3 if n < k { 4 return [] 5 } 6 var combo: [Int] = [] 7 var results: [[Int]] = [] 8 for i in 1...n { 9 backtacking(i, n, k, &combo, &results) 10 } 11 return results 12 } 13 14 private func backtacking(_ begin: Int, _ end: Int, _ limit: Int, _ combo: inout [Int], _ results: inout [[Int]]) { 15 let remains = end - begin + 1 16 if combo.count + remains >= limit { 17 combo.append(begin) 18 if combo.count == limit { 19 results.append(combo) 20 } else { 21 for i in 1..<remains { 22 backtacking(begin + i, end, limit, &combo, &results) 23 } 24 } 25 combo.removeLast() 26 } 27 } 28 }
116ms
1 class Solution { 2 3 func combine(_ n: Int, _ k: Int) -> [[Int]] { 4 guard n > 0 else { 5 return [] 6 } 7 var result : [[Int]] = [] 8 var nums : [Int] = Array(repeating: 0, count: k) 9 combineNext(lastIndex: 1,leftCount: k, numsIndex: 0, result: &result, nums: &nums, maxN: n) 10 return result 11 } 12 private func combineNext(lastIndex:Int,leftCount:Int,numsIndex:Int , result : inout [[Int]] , nums : inout [Int] , maxN : Int) { 13 if leftCount == 0{ 14 result.append(nums) 15 return 16 } 17 if lastIndex>maxN { 18 return 19 } 20 21 for idx in lastIndex...maxN { 22 nums[numsIndex] = idx 23 combineNext(lastIndex: idx+1, leftCount: leftCount-1,numsIndex: numsIndex+1, result: &result, nums: &nums, maxN: maxN) 24 } 25 } 26 }
204ms
1 class Solution { 2 func combine(_ n: Int, _ k: Int) -> [[Int]] { 3 guard k <= n else { return [] } 4 guard k > 0 else { return [[]] } 5 guard k > 1 else { return (1...n).map { [$0] } } 6 7 return combine(n-1, k) + combine(n-1, k-1).map { $0 + [n] } 8 } 9 }
152ms
1 class Solution {
2 var list:[[Int]] = [[Int]]()
3 var n:Int = 0
4 func combine(_ n: Int, _ k: Int) -> [[Int]] {
5 self.n = n
6 var comb:[Int] = [Int]()
7 combines(comb,1, k)
8 return list
9 }
10
11 func combines(_ temp:[Int],_ count:Int,_ k:Int)
12 {
13 var temp = temp
14 if k == 0
15 {
16 list.append(temp)
17 return
18 }
19 if count + k - 1 > n { return}
20 temp.append(count)
21 combines(temp, count + 1, k - 1)
22 temp.removeLast()
23 combines(temp, count + 1, k)
24 }
25 }
