使用Python进行计算和编程简介

Question

I am trying to solve Finger Exercise 3.1, and I can't figure out what I am doing wrong here. When I enter '1' as the integer, it returns 0 and 0.

I am a complete newbie to programming and Stack Overflow, so I'm not sure if I am doing this correctly, but I figured I would give it a shot.

This is the problem: Write a program that asks the user to enter an integer and prints two integers, root and pwr, such that 0 < pwr < 6 and root**pwr is equal to the integer entered by the user. If no such pair of integers exists, it should print a message to that effect.

And here is my solution thus far:

x = int(raw_input('Enter a positive integer: '))
root = 0
pwr = 0
while pwr < 6:
    pwr += 1
    while root**pwr < x:
        root += 1
if root**pwr == x:
    print "The root is " + str(root) + " and the power is " + str(pwr)
else:
    print "No such pair of integers exists."

How can I fix my code so that it returns the correct integers? What am I doing wrong here? What logic am I missing?

Answer 1

One problem is that, while you do have conditions that end your loops, they will always go all the way up to the maximum allowed condition. You could solve that with break or, as shown, by using return in a function. Also, instead of using a counter, use the xrange() function ( range() in Python 3).

>>> def p(num):
...     for power in xrange(6):
...         for root in xrange(num/2+1):
...             if root**power==num:
...                 return root, power
...
>>> r, pwr = p(8)
>>> print 'The root is', r, 'and the power is', pwr
The root is 2 and the power is 3

Answer 2

Albeit not very idiomatic for Python, you are close to a correct answer.

The first problem is that you never reset root so you will execute the inner loop only once. Moving root = 0 to the outer loop should fix it.

The second error is that you never break off the loop when you reach the condition you seek. Moving the test to inside the loop will fix this.

Lets see how are we doing so far:

x = int(raw_input('Enter a positive integer: '))
pwr = 0
while pwr < 6:
    root = 0
    pwr += 1
    while root**pwr < x:
        root += 1
        if root**pwr == x:
            print "The root is {} and the power is {}".fornat(
               root, pwr
            )
else:
    print "No such pair of integers exists."

This outputs:

Enter a positive integer: 16
The root is 16 and the power is 1
The root is 4 and the power is 2
The root is 2 and the power is 4
No such pair of integers exists.

Since it is a learning exercise, I will let you figure out and fix other problems with your code.