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Feature/chapter greedy swift (#720)
* feat: add Swift codes for greedy_algorithm article * feat: add Swift codes for fractional_knapsack_problem article * feat: add Swift codes for max_capacity_problem article * feat: add Swift codes for max_product_cutting_problem article
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5 changed files with 202 additions and 0 deletions
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@ -93,6 +93,11 @@ let package = Package(
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.executable(name: "coin_change", targets: ["coin_change"]),
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.executable(name: "coin_change", targets: ["coin_change"]),
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.executable(name: "coin_change_ii", targets: ["coin_change_ii"]),
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.executable(name: "coin_change_ii", targets: ["coin_change_ii"]),
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.executable(name: "edit_distance", targets: ["edit_distance"]),
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.executable(name: "edit_distance", targets: ["edit_distance"]),
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// chapter_greedy
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.executable(name: "coin_change_greedy", targets: ["coin_change_greedy"]),
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.executable(name: "fractional_knapsack", targets: ["fractional_knapsack"]),
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.executable(name: "max_capacity", targets: ["max_capacity"]),
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.executable(name: "max_product_cutting", targets: ["max_product_cutting"]),
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],
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],
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targets: [
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targets: [
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// helper
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// helper
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@ -187,5 +192,10 @@ let package = Package(
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.executableTarget(name: "coin_change", path: "chapter_dynamic_programming", sources: ["coin_change.swift"]),
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.executableTarget(name: "coin_change", path: "chapter_dynamic_programming", sources: ["coin_change.swift"]),
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.executableTarget(name: "coin_change_ii", path: "chapter_dynamic_programming", sources: ["coin_change_ii.swift"]),
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.executableTarget(name: "coin_change_ii", path: "chapter_dynamic_programming", sources: ["coin_change_ii.swift"]),
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.executableTarget(name: "edit_distance", path: "chapter_dynamic_programming", sources: ["edit_distance.swift"]),
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.executableTarget(name: "edit_distance", path: "chapter_dynamic_programming", sources: ["edit_distance.swift"]),
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// chapter_greedy
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.executableTarget(name: "coin_change_greedy", path: "chapter_greedy", sources: ["coin_change_greedy.swift"]),
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.executableTarget(name: "fractional_knapsack", path: "chapter_greedy", sources: ["fractional_knapsack.swift"]),
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.executableTarget(name: "max_capacity", path: "chapter_greedy", sources: ["max_capacity.swift"]),
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.executableTarget(name: "max_product_cutting", path: "chapter_greedy", sources: ["max_product_cutting.swift"]),
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]
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]
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)
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)
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54
codes/swift/chapter_greedy/coin_change_greedy.swift
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54
codes/swift/chapter_greedy/coin_change_greedy.swift
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@ -0,0 +1,54 @@
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/**
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* File: coin_change_greedy.swift
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* Created Time: 2023-09-03
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* Author: nuomi1 (nuomi1@qq.com)
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*/
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/* 零钱兑换:贪心 */
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func coinChangeGreedy(coins: [Int], amt: Int) -> Int {
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// 假设 coins 列表有序
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var i = coins.count - 1
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var count = 0
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var amt = amt
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// 循环进行贪心选择,直到无剩余金额
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while amt > 0 {
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// 找到小于且最接近剩余金额的硬币
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while i > 0 && coins[i] > amt {
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i -= 1
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}
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// 选择 coins[i]
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amt -= coins[i]
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count += 1
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}
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// 若未找到可行方案,则返回 -1
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return amt == 0 ? count : -1
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}
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@main
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enum CoinChangeGreedy {
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/* Driver Code */
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static func main() {
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// 贪心:能够保证找到全局最优解
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var coins = [1, 5, 10, 20, 50, 100]
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var amt = 186
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var res = coinChangeGreedy(coins: coins, amt: amt)
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print("\ncoins = \(coins), amount = \(amt)")
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print("凑到 \(amt) 所需的最少硬币数量为 \(res)")
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// 贪心:无法保证找到全局最优解
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coins = [1, 20, 50]
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amt = 60
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res = coinChangeGreedy(coins: coins, amt: amt)
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print("\ncoins = \(coins), amount = \(amt)")
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print("凑到 \(amt) 所需的最少硬币数量为 \(res)")
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print("实际上需要的最少数量为 3 ,即 20 + 20 + 20")
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// 贪心:无法保证找到全局最优解
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coins = [1, 49, 50]
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amt = 98
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res = coinChangeGreedy(coins: coins, amt: amt)
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print("\ncoins = \(coins), amount = \(amt)")
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print("凑到 \(amt) 所需的最少硬币数量为 \(res)")
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print("实际上需要的最少数量为 2 ,即 49 + 49")
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}
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}
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57
codes/swift/chapter_greedy/fractional_knapsack.swift
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57
codes/swift/chapter_greedy/fractional_knapsack.swift
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/**
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* File: fractional_knapsack.swift
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* Created Time: 2023-09-03
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* Author: nuomi1 (nuomi1@qq.com)
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*/
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// 物品
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struct Item {
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var w: Int // 物品重量
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var v: Int // 物品价值
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init(w: Int, v: Int) {
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self.w = w
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self.v = v
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}
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}
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/* 分数背包:贪心 */
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func fractionalKnapsack(wgt: [Int], val: [Int], cap: Int) -> Double {
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// 创建物品列表,包含两个属性:重量、价值
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var items = zip(wgt, val).map { Item(w: $0, v: $1) }
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// 按照单位价值 item.v / item.w 从高到低进行排序
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items.sort(by: { -(Double($0.v) / Double($0.w)) < -(Double($1.v) / Double($1.w)) })
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// 循环贪心选择
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var res = 0.0
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var cap = cap
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for item in items {
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if item.w <= cap {
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// 若剩余容量充足,则将当前物品整个装进背包
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res += Double(item.v)
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cap -= item.w
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} else {
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// 若剩余容量不足,则将当前物品的一部分装进背包
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res += Double(item.v) / Double(item.w) * Double(cap)
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// 已无剩余容量,因此跳出循环
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break
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}
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}
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return res
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}
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@main
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enum FractionalKnapsack {
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/* Driver Code */
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static func main() {
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// 物品重量
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let wgt = [10, 20, 30, 40, 50]
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// 物品价值
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let val = [50, 120, 150, 210, 240]
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// 背包容量
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let cap = 50
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// 贪心算法
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let res = fractionalKnapsack(wgt: wgt, val: val, cap: cap)
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print("不超过背包容量的最大物品价值为 \(res)")
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}
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}
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38
codes/swift/chapter_greedy/max_capacity.swift
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38
codes/swift/chapter_greedy/max_capacity.swift
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/**
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* File: max_capacity.swift
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* Created Time: 2023-09-03
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* Author: nuomi1 (nuomi1@qq.com)
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*/
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/* 最大容量:贪心 */
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func maxCapacity(ht: [Int]) -> Int {
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// 初始化 i, j 分列数组两端
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var i = 0, j = ht.count - 1
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// 初始最大容量为 0
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var res = 0
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// 循环贪心选择,直至两板相遇
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while i < j {
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// 更新最大容量
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let cap = min(ht[i], ht[j]) * (j - i)
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res = max(res, cap)
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// 向内移动短板
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if ht[i] < ht[j] {
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i += 1
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} else {
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j -= 1
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}
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}
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return res
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}
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@main
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enum MaxCapacity {
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/* Driver Code */
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static func main() {
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let ht = [3, 8, 5, 2, 7, 7, 3, 4]
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// 贪心算法
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let res = maxCapacity(ht: ht)
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print("最大容量为 \(res)")
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}
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}
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43
codes/swift/chapter_greedy/max_product_cutting.swift
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43
codes/swift/chapter_greedy/max_product_cutting.swift
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/**
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* File: max_product_cutting.swift
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* Created Time: 2023-09-03
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* Author: nuomi1 (nuomi1@qq.com)
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*/
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import Foundation
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func pow(_ x: Int, _ y: Int) -> Int {
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Int(Double(truncating: pow(Decimal(x), y) as NSDecimalNumber))
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}
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/* 最大切分乘积:贪心 */
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func maxProductCutting(n: Int) -> Int {
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// 当 n <= 3 时,必须切分出一个 1
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if n <= 3 {
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return 1 * (n - 1)
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}
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// 贪心地切分出 3 ,a 为 3 的个数,b 为余数
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let a = n / 3
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let b = n % 3
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if b == 1 {
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// 当余数为 1 时,将一对 1 * 3 转化为 2 * 2
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return pow(3, a - 1) * 2 * 2
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}
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if b == 2 {
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// 当余数为 2 时,不做处理
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return pow(3, a) * 2
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}
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// 当余数为 0 时,不做处理
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return pow(3, a)
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}
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@main
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enum MaxProductCutting {
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static func main() {
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let n = 58
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// 贪心算法
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let res = maxProductCutting(n: n)
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print("最大切分乘积为 \(res)")
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}
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}
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