（深坑）问题收集

1.斐波那契数列问题

• 定义：

f(1) = 1;
f(2) = 1;
f(n) = f(n-1) + f(n-2);

• 代码：

# 方法一：递归实现，这种实现方式当n很大时，会有栈溢出问题，内存占用大
def fib(n):
    if n == 1 or n == 2:
        return 1;
    else:
        return fib(n-1) + fib(n-2);

# 方法二：循环实现
def fib(n):
    if n == 1 or n == 2:
        return 1;
    i, first, second = 2, 0, 1;
    while i <= n:
        first, second = second, first + second;
        i = i+1;
    return second;

2.反转单词

例：
"how are you" -> "you are how"

# 方法一：将字符串分割成全部单词组成的列表，再利用切片
# 由后向前遍历，用空格连接每个单词，组成新的字符串并返回；
def reverse_words(s):
    return " ".join(s.split()[::-1])


# 方法二：先反转整个字符串，再反转每个单词
def reverse_words2(s):
    # 整个字符串整体反转
    # how are you -> uoy era woh
    list = s[::-1].split()
    # 对每一个元素进行反转
    # uoy era woh -> you are how
    list2 = [i[::-1] for i in list]
    return " ".join(list2)

3.快速排序

def quick_sort(list, first, last):
    if first >= last:
        return;
    key = list[first];
    i, j = first, last;
    while j > i:
        while j > i:
            if list[j] >= key:
                j = j - 1;
            else:
                break;
        if j > i:
            list[i],list[j] = list[j], key;
        while j > i:
            if list[i] <= key:
                i = i + 1;
            else:
                break;
        if j > i:
            list[i],list[j] = key, list[i];
    quick_sort(list, first, i-1);
    quick_sort(list, i+1, last);