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Combinations.swift
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Combinations.swift
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//
// Combinations.swift
// LeetCode
//
// Created by 榛庤档澶儙 on 05/01/2018.
// Copyright 漏 2018 lizhaotailang. All rights reserved.
//
// Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.
//
// For example,
// If n = 4 and k = 2, a solution is:
//
// [
// [2,4],
// [3,4],
// [2,3],
// [1,2],
// [1,3],
// [1,4],
// ]
//
// See [CombinationsTests](./LeetCodeTests/CombinationsTests.swift) for test cases.
//
import Foundation
class Combinations {
// Recursive Solution.
// Accepted.
// func combine(_ n: Int, _ k: Int) -> [[Int]] {
// var results = Array<Array<Int>>.init()
// if n == 0 || k == 0 || k > n {
// return results
// }
//
// if k == 1 {
// var i = 1
// while i <= n {
// results.append([i])
//
// i += 1
// }
//
// return results
// }
//
// for list in combine(n, k - 1) {
// var i = list[list.count - 1]
// while i < n {
// var tmp = Array<Int>.init()
// tmp.append(contentsOf: list)
// tmp.append(i + 1)
// results.append(tmp)
//
// i += 1
// }
// }
//
// return results
// }
// Iterative Solution.
// Accepted.
func combine(_ n: Int, _ k: Int) -> [[Int]] {
var results = Array<Array<Int>>.init()
if n == 0 || k == 0 || k > n {
return results
}
var i = 1
while i <= n + 1 - k {
results.append([i])
i += 1
}
i = 2
while i <= k {
var tmp = Array<Array<Int>>.init()
for list in results {
var m = list[list.count - 1] + 1
while m <= n - (k - i) {
var newList = Array<Int>.init()
newList.append(contentsOf: list)
newList.append(m)
tmp.append(newList)
m += 1
}
}
results = tmp
i += 1
}
return results
}
}