From 89679a4a13bd1ce96d17d1b43fe3416d944f482a Mon Sep 17 00:00:00 2001
From: curtishd <131777542+curtishd@users.noreply.github.com>
Date: Mon, 4 Mar 2024 00:10:34 +0800
Subject: [PATCH] Add kotlin codes for the chapter of greedy (#1103)

* feat(kotlin): add kotlin code for dynamic programming.

* Update knapsack.kt

* feat(kotlin): add kotlin codes for graph.

* style(kotlin): reformatted the codes.

* feat(kotlin): add kotlin codes for the chapter of greedy.

* Update max_product_cutting.kt
---
 .../chapter_greedy/coin_change_greedy.kt      | 53 +++++++++++++++++
 .../chapter_greedy/fractional_knapsack.kt     | 57 +++++++++++++++++++
 codes/kotlin/chapter_greedy/max_capacity.kt   | 41 +++++++++++++
 .../chapter_greedy/max_product_cutting.kt     | 39 +++++++++++++
 4 files changed, 190 insertions(+)
 create mode 100644 codes/kotlin/chapter_greedy/coin_change_greedy.kt
 create mode 100644 codes/kotlin/chapter_greedy/fractional_knapsack.kt
 create mode 100644 codes/kotlin/chapter_greedy/max_capacity.kt
 create mode 100644 codes/kotlin/chapter_greedy/max_product_cutting.kt

diff --git a/codes/kotlin/chapter_greedy/coin_change_greedy.kt b/codes/kotlin/chapter_greedy/coin_change_greedy.kt
new file mode 100644
index 000000000..32fce1f67
--- /dev/null
+++ b/codes/kotlin/chapter_greedy/coin_change_greedy.kt
@@ -0,0 +1,53 @@
+/**
+ * File: coin_change_greedy.kt
+ * Created Time: 2024-01-25
+ * Author: curtishd (1023632660@qq.com)
+ */
+
+package chapter_greedy
+
+/* 零钱兑换：贪心 */
+fun coinChangeGreedy(coins: IntArray, amt: Int): Int {
+    // 假设 coins 列表有序
+    var am = amt
+    var i = coins.size - 1
+    var count = 0
+    // 循环进行贪心选择，直到无剩余金额
+    while (am > 0) {
+        // 找到小于且最接近剩余金额的硬币
+        while (i > 0 && coins[i] > am) {
+            i--
+        }
+        // 选择 coins[i]
+        am -= coins[i]
+        count++
+    }
+    // 若未找到可行方案，则返回 -1
+    return if (am == 0) count else -1
+}
+
+/* Driver Code */
+fun main() {
+    // 贪心：能够保证找到全局最优解
+    var coins = intArrayOf(1, 5, 10, 20, 50, 100)
+    var amt = 186
+    var res = coinChangeGreedy(coins, amt)
+    println("\ncoins = ${coins.contentToString()}, amt = $amt")
+    println("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 = intArrayOf(1, 20, 50)
+    amt = 60
+    res = coinChangeGreedy(coins, amt)
+    println("\ncoins = ${coins.contentToString()}, amt = $amt")
+    println("凑到 $amt 所需的最少硬币数量为 $res")
+    println("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 = intArrayOf(1, 49, 50)
+    amt = 98
+    res = coinChangeGreedy(coins, amt)
+    println("\ncoins = ${coins.contentToString()}, amt = $amt")
+    println("凑到 $amt 所需的最少硬币数量为 $res")
+    println("实际上需要的最少数量为 2 ，即 49 + 49")
+}
\ No newline at end of file
diff --git a/codes/kotlin/chapter_greedy/fractional_knapsack.kt b/codes/kotlin/chapter_greedy/fractional_knapsack.kt
new file mode 100644
index 000000000..0b375b66c
--- /dev/null
+++ b/codes/kotlin/chapter_greedy/fractional_knapsack.kt
@@ -0,0 +1,57 @@
+/**
+ * File: fractional_knapsack.kt
+ * Created Time: 2024-01-25
+ * Author: curtishd (1023632660@qq.com)
+ */
+
+package chapter_greedy
+
+import java.util.*
+
+/* 物品 */
+class Item(
+    val w: Int, // 物品
+    val v: Int // 物品价值
+)
+
+/* 分数背包：贪心 */
+fun fractionalKnapsack(
+    wgt: IntArray,
+    value: IntArray,
+    c: Int
+): Double {
+    // 创建物品列表，包含两个属性：重量、价值
+    var cap = c
+    val items = arrayOfNulls<Item>(wgt.size)
+    for (i in wgt.indices) {
+        items[i] = Item(wgt[i], value[i])
+    }
+    // 按照单位价值 item.v / item.w 从高到低进行排序
+    Arrays.sort(items, Comparator.comparingDouble { item: Item -> -(item.v.toDouble() / item.w) })
+    // 循环贪心选择
+    var res = 0.0
+    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 += item.v.toDouble()
+            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 += item.v.toDouble() / item.w * cap
+            // 已无剩余容量，因此跳出循环
+            break
+        }
+    }
+    return res
+}
+
+/* Driver Code */
+fun main() {
+    val wgt = intArrayOf(10, 20, 30, 40, 50)
+    val values = intArrayOf(50, 120, 150, 210, 240)
+    val cap = 50
+
+    // 贪心算法
+    val res = fractionalKnapsack(wgt, values, cap)
+    println("不超过背包容量的最大物品价值为 $res")
+}
\ No newline at end of file
diff --git a/codes/kotlin/chapter_greedy/max_capacity.kt b/codes/kotlin/chapter_greedy/max_capacity.kt
new file mode 100644
index 000000000..ea9edfe27
--- /dev/null
+++ b/codes/kotlin/chapter_greedy/max_capacity.kt
@@ -0,0 +1,41 @@
+/**
+ * File: max_capacity.kt
+ * Created Time: 2024-01-25
+ * Author: curtishd (1023632660@qq.com)
+ */
+
+package chapter_greedy
+
+import kotlin.math.max
+import kotlin.math.min
+
+/* 最大容量：贪心 */
+fun maxCapacity(ht: IntArray): Int {
+    // 初始化 i, j，使其分列数组两端
+    var i = 0
+    var j = ht.size - 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
+        val cap = (min(ht[i].toDouble(), ht[j].toDouble()) * (j - i)).toInt()
+        res = max(res.toDouble(), cap.toDouble()).toInt()
+        // 向内移动短板
+        if (ht[i] < ht[j]) {
+            i++
+        } else {
+            j--
+        }
+    }
+    return res
+}
+
+/* Driver Code */
+fun main() {
+    val ht = intArrayOf(3, 8, 5, 2, 7, 7, 3, 4)
+
+    // 贪心算法
+    val res = maxCapacity(ht)
+    println("最大容量为 $res")
+}
\ No newline at end of file
diff --git a/codes/kotlin/chapter_greedy/max_product_cutting.kt b/codes/kotlin/chapter_greedy/max_product_cutting.kt
new file mode 100644
index 000000000..9a24ce756
--- /dev/null
+++ b/codes/kotlin/chapter_greedy/max_product_cutting.kt
@@ -0,0 +1,39 @@
+/**
+ * File: max_product_cutting.kt
+ * Created Time: 2024-01-25
+ * Author: curtishd (1023632660@qq.com)
+ */
+
+package chapter_greedy
+
+import kotlin.math.pow
+
+/* 最大切分乘积：贪心 */
+fun 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
+    val a = n / 3
+    val b = n % 3
+    if (b == 1) {
+        // 当余数为 1 时，将一对 1 * 3 转化为 2 * 2
+        return 3.0.pow((a - 1).toDouble()).toInt() * 2 * 2
+    }
+    if (b == 2) {
+        // 当余数为 2 时，不做处理
+        return 3.0.pow(a.toDouble()).toInt() * 2 * 2
+    }
+    // 当余数为 0 时，不做处理
+    return 3.0.pow(a.toDouble()).toInt()
+}
+
+/* Driver Code */
+fun main() {
+    val n = 58
+
+    // 贪心算法
+    val res = maxProductCutting(n)
+    println("最大切分乘积为 $res")
+}