不使用内置函数也不需要额外的数组来颠倒一个句子

def reverse_sentence(sentence):
    # 将句子转换为字符列表以便操作
    chars = list(sentence)
    left, right = 0, len(chars) - 1
    
    # 颠倒整个字符列表
    while left < right:
        chars[left], chars[right] = chars[right], chars[left]
        left += 1
        right -= 1
    
    # 再次遍历字符列表，颠倒每个单词内部的字符顺序
    start = 0
    for i in range(len(chars)):
        if chars[i] == ' ' or i == len(chars) - 1:
            end = i if chars[i] != ' ' else i - 1
            while start < end:
                chars[start], chars[end] = chars[end], chars[start]
                start += 1
                end -= 1
            start = i + 1
    
    # 将字符列表转换回字符串
    return ''.join(chars)

# 测试
sentence = "Hello World"
print(reverse_sentence(sentence))  # 输出: "World Hello"