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

codes/swift/Package.swift

@@ -93,6 +93,11 @@ let package = Package(
         .executable(name: "coin_change", targets: ["coin_change"]),
         .executable(name: "coin_change_ii", targets: ["coin_change_ii"]),
         .executable(name: "edit_distance", targets: ["edit_distance"]),
+        // chapter_greedy
+        .executable(name: "coin_change_greedy", targets: ["coin_change_greedy"]),
+        .executable(name: "fractional_knapsack", targets: ["fractional_knapsack"]),
+        .executable(name: "max_capacity", targets: ["max_capacity"]),
+        .executable(name: "max_product_cutting", targets: ["max_product_cutting"]),
     ],
     targets: [
         // helper
@@ -187,5 +192,10 @@ let package = Package(
         .executableTarget(name: "coin_change", path: "chapter_dynamic_programming", sources: ["coin_change.swift"]),
         .executableTarget(name: "coin_change_ii", path: "chapter_dynamic_programming", sources: ["coin_change_ii.swift"]),
         .executableTarget(name: "edit_distance", path: "chapter_dynamic_programming", sources: ["edit_distance.swift"]),
+        // chapter_greedy
+        .executableTarget(name: "coin_change_greedy", path: "chapter_greedy", sources: ["coin_change_greedy.swift"]),
+        .executableTarget(name: "fractional_knapsack", path: "chapter_greedy", sources: ["fractional_knapsack.swift"]),
+        .executableTarget(name: "max_capacity", path: "chapter_greedy", sources: ["max_capacity.swift"]),
+        .executableTarget(name: "max_product_cutting", path: "chapter_greedy", sources: ["max_product_cutting.swift"]),
     ]
 )

codes/swift/chapter_greedy/coin_change_greedy.swift

@@ -0,0 +1,54 @@
+/**
+ * File: coin_change_greedy.swift
+ * Created Time: 2023-09-03
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+/* 零钱兑换：贪心 */
+func coinChangeGreedy(coins: [Int], amt: Int) -> Int {
+    // 假设 coins 列表有序
+    var i = coins.count - 1
+    var count = 0
+    var amt = amt
+    // 循环进行贪心选择，直到无剩余金额
+    while amt > 0 {
+        // 找到小于且最接近剩余金额的硬币
+        while i > 0 && coins[i] > amt {
+            i -= 1
+        }
+        // 选择 coins[i]
+        amt -= coins[i]
+        count += 1
+    }
+    // 若未找到可行方案，则返回 -1
+    return amt == 0 ? count : -1
+}
+
+@main
+enum CoinChangeGreedy {
+    /* Driver Code */
+    static func main() {
+        // 贪心：能够保证找到全局最优解
+        var coins = [1, 5, 10, 20, 50, 100]
+        var amt = 186
+        var res = coinChangeGreedy(coins: coins, amt: amt)
+        print("\ncoins = \(coins), amount = \(amt)")
+        print("凑到 \(amt) 所需的最少硬币数量为 \(res)")
+
+        // 贪心：无法保证找到全局最优解
+        coins = [1, 20, 50]
+        amt = 60
+        res = coinChangeGreedy(coins: coins, amt: amt)
+        print("\ncoins = \(coins), amount = \(amt)")
+        print("凑到 \(amt) 所需的最少硬币数量为 \(res)")
+        print("实际上需要的最少数量为 3 ，即 20 + 20 + 20")
+
+        // 贪心：无法保证找到全局最优解
+        coins = [1, 49, 50]
+        amt = 98
+        res = coinChangeGreedy(coins: coins, amt: amt)
+        print("\ncoins = \(coins), amount = \(amt)")
+        print("凑到 \(amt) 所需的最少硬币数量为 \(res)")
+        print("实际上需要的最少数量为 2 ，即 49 + 49")
+    }
+}

codes/swift/chapter_greedy/fractional_knapsack.swift

@@ -0,0 +1,57 @@
+/**
+ * File: fractional_knapsack.swift
+ * Created Time: 2023-09-03
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+// 物品
+struct Item {
+    var w: Int // 物品重量
+    var v: Int // 物品价值
+
+    init(w: Int, v: Int) {
+        self.w = w
+        self.v = v
+    }
+}
+
+/* 分数背包：贪心 */
+func fractionalKnapsack(wgt: [Int], val: [Int], cap: Int) -> Double {
+    // 创建物品列表，包含两个属性：重量、价值
+    var items = zip(wgt, val).map { Item(w: $0, v: $1) }
+    // 按照单位价值 item.v / item.w 从高到低进行排序
+    items.sort(by: { -(Double($0.v) / Double($0.w)) < -(Double($1.v) / Double($1.w)) })
+    // 循环贪心选择
+    var res = 0.0
+    var cap = cap
+    for item in items {
+        if item.w <= cap {
+            // 若剩余容量充足，则将当前物品整个装进背包
+            res += Double(item.v)
+            cap -= item.w
+        } else {
+            // 若剩余容量不足，则将当前物品的一部分装进背包
+            res += Double(item.v) / Double(item.w) * Double(cap)
+            // 已无剩余容量，因此跳出循环
+            break
+        }
+    }
+    return res
+}
+
+@main
+enum FractionalKnapsack {
+    /* Driver Code */
+    static func main() {
+        // 物品重量
+        let wgt = [10, 20, 30, 40, 50]
+        // 物品价值
+        let val = [50, 120, 150, 210, 240]
+        // 背包容量
+        let cap = 50
+
+        // 贪心算法
+        let res = fractionalKnapsack(wgt: wgt, val: val, cap: cap)
+        print("不超过背包容量的最大物品价值为 \(res)")
+    }
+}

codes/swift/chapter_greedy/max_capacity.swift

@@ -0,0 +1,38 @@
+/**
+ * File: max_capacity.swift
+ * Created Time: 2023-09-03
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+/* 最大容量：贪心 */
+func maxCapacity(ht: [Int]) -> Int {
+    // 初始化 i, j 分列数组两端
+    var i = 0, j = ht.count - 1
+    // 初始最大容量为 0
+    var res = 0
+    // 循环贪心选择，直至两板相遇
+    while i < j {
+        // 更新最大容量
+        let cap = min(ht[i], ht[j]) * (j - i)
+        res = max(res, cap)
+        // 向内移动短板
+        if ht[i] < ht[j] {
+            i += 1
+        } else {
+            j -= 1
+        }
+    }
+    return res
+}
+
+@main
+enum MaxCapacity {
+    /* Driver Code */
+    static func main() {
+        let ht = [3, 8, 5, 2, 7, 7, 3, 4]
+
+        // 贪心算法
+        let res = maxCapacity(ht: ht)
+        print("最大容量为 \(res)")
+    }
+}

codes/swift/chapter_greedy/max_product_cutting.swift

@@ -0,0 +1,43 @@
+/**
+ * File: max_product_cutting.swift
+ * Created Time: 2023-09-03
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+import Foundation
+
+func pow(_ x: Int, _ y: Int) -> Int {
+    Int(Double(truncating: pow(Decimal(x), y) as NSDecimalNumber))
+}
+
+/* 最大切分乘积：贪心 */
+func maxProductCutting(n: Int) -> Int {
+    // 当 n <= 3 时，必须切分出一个 1
+    if n <= 3 {
+        return 1 * (n - 1)
+    }
+    // 贪心地切分出 3 ，a 为 3 的个数，b 为余数
+    let a = n / 3
+    let b = n % 3
+    if b == 1 {
+        // 当余数为 1 时，将一对 1 * 3 转化为 2 * 2
+        return pow(3, a - 1) * 2 * 2
+    }
+    if b == 2 {
+        // 当余数为 2 时，不做处理
+        return pow(3, a) * 2
+    }
+    // 当余数为 0 时，不做处理
+    return pow(3, a)
+}
+
+@main
+enum MaxProductCutting {
+    static func main() {
+        let n = 58
+
+        // 贪心算法
+        let res = maxProductCutting(n: n)
+        print("最大切分乘积为 \(res)")
+    }
+}