How to Sort Three Numbers and Generate Fibonacci Sequences in Python

Example 1

Problem: Input three integers x, y, z and output them in ascending order.

Analysis: Compare x with y and swap if x > y, then compare x with z and swap if x > z, ensuring x holds the smallest value.

<code>#!/usr/bin/python
# -*- coding: UTF-8 -*-

l = []
for i in range(3):
    x = int(raw_input('integer:\n'))
    l.append(x)
l.sort()
print l
</code>

Sample input and output:

<code>integer:
8
integer:
5
integer:
6
[5, 6, 8]
</code>

Example 2

Problem: Generate Fibonacci numbers.

Analysis: The Fibonacci sequence is defined recursively: F0 = 0, F1 = 1, Fn = F(n‑1) + F(n‑2) for n ≥ 2.

<code>F0 = 0    (n=0)

F1 = 1    (n=1)

Fn = F[n-1] + F[n-2] (n>=2)
</code>

Method 1 – Iterative:

<code>#!/usr/bin/python
# -*- coding: UTF-8 -*-

def fib(n):
    a, b = 1, 1
    for i in range(n-1):
        a, b = b, a+b
    return a

print fib(10)   # 55
</code>

Method 2 – Recursive:

<code>#!/usr/bin/python
# -*- coding: UTF-8 -*-

def fib(n):
    if n == 1 or n == 2:
        return 1
    return fib(n-1) + fib(n-2)

print fib(10)   # 55
</code>

Method 3 – Return full list:

<code>#!/usr/bin/python
# -*- coding: UTF-8 -*-

def fib(n):
    if n == 1:
        return [1]
    if n == 2:
        return [1, 1]
    fibs = [1, 1]
    for i in range(2, n):
        fibs.append(fibs[-1] + fibs[-2])
    return fibs

print fib(10)   # [1, 1, 2, 3, 5, 8, 13, 21, 34, 55]
</code>