Add the chapter of greedy. (#633)

Add the section of fractional knapsack.

codes/python/chapter_greedy/coin_change_greedy.py

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+"""
+File: coin_change_greedy.py
+Created Time: 2023-07-18
+Author: Krahets (krahets@163.com)
+"""
+
+
+def coin_change_greedy(coins: list[int], amt: int) -> int:
+    """零钱兑换：贪心"""
+    # 假设 coins 列表有序
+    i = len(coins) - 1
+    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 -= 1
+        # 选择 coins[i]
+        amt -= coins[i]
+        count += 1
+    # 若未找到可行方案，则返回 -1
+    return count if amt == 0 else -1
+
+
+"""Driver Code"""
+if __name__ == "__main__":
+    # 贪心：能够保证找到全局最优解
+    coins = [1, 5, 10, 20, 50, 100]
+    amt = 186
+    res = coin_change_greedy(coins, amt)
+    print(f"\ncoins = {coins}, amt = {amt}")
+    print(f"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 = coin_change_greedy(coins, amt)
+    print(f"\ncoins = {coins}, amt = {amt}")
+    print(f"凑到 {amt} 所需的最少硬币数量为 {res}")
+    print(f"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 = coin_change_greedy(coins, amt)
+    print(f"\ncoins = {coins}, amt = {amt}")
+    print(f"凑到 {amt} 所需的最少硬币数量为 {res}")
+    print(f"实际上需要的最少数量为 2 ，即 49 + 49")