Add the chapter of greedy. (#633)

Add the section of fractional knapsack.

codes/cpp/chapter_greedy/coin_change_greedy.cpp

@@ -0,0 +1,60 @@
+/**
+ * File: coin_change_greedy.cpp
+ * Created Time: 2023-07-20
+ * Author: Krahets (krahets@163.com)
+ */
+
+#include "../utils/common.hpp"
+
+/* 零钱兑换：贪心 */
+int coinChangeGreedy(vector<int> &coins, int amt) {
+    // 假设 coins 列表有序
+    int i = coins.size() - 1;
+    int count = 0;
+    // 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 (coins[i] > amt) {
+            i--;
+        }
+        // 选择 coins[i]
+        amt -= coins[i];
+        count++;
+    }
+    // 若未找到可行方案，则返回 -1
+    return amt == 0 ? count : -1;
+}
+
+/* Driver Code */
+int main() {
+    // 贪心：能够保证找到全局最优解
+    vector<int> coins = {1, 5, 10, 20, 50, 100};
+    int amt = 186;
+    int res = coinChangeGreedy(coins, amt);
+    cout << "\ncoins = ";
+    printVector(coins);
+    cout << "amt = " << amt << endl;
+    cout << "凑到 " << amt << " 所需的最少硬币数量为 " << res << endl;
+
+    // 贪心：无法保证找到全局最优解
+    coins = {1, 20, 50};
+    amt = 60;
+    res = coinChangeGreedy(coins, amt);
+    cout << "\ncoins = [";
+    printVector(coins);
+    cout << "amt = " << amt << endl;
+    cout << "凑到 " << amt << " 所需的最少硬币数量为 " << res << endl;
+    cout << "实际上需要的最少数量为 3 ，即 20 + 20 + 20" << endl;
+
+    // 贪心：无法保证找到全局最优解
+    coins = {1, 49, 50};
+    amt = 98;
+    res = coinChangeGreedy(coins, amt);
+    cout << "\ncoins = [";
+    printVector(coins);
+    cout << "amt = " << amt << endl;
+    cout << "凑到 " << amt << " 所需的最少硬币数量为 " << res << endl;
+    cout << "实际上需要的最少数量为 2 ，即 49 + 49" << endl;
+
+    return 0;
+}