如何在Python列表中使用变量求解连续数字最大乘积问题

Let's walk through how to tackle this problem using Python's list functionality—super straightforward once you break it down.

Step 1: Convert the big number string to a list of integers #

First, we need to turn that giant 1000-digit string into a list of individual integers. Lists let us easily access elements by index, which is perfect for grabbing adjacent digits later. Here's how:

# Your full 1000-digit number string (truncated here for brevity)
num_str = "73167176531330624919225119674426574742355349194934969835203127745063262395783180169848018694788518438586156078911294949545950173795833195285320880551112540698747158523863050715693290963295227443043557668966489504452445231617318564030987111217223831136222989342338030813533627661428280644448664523874930358907296290491560440772390713810515859307960..."
# Convert each character to an integer, store in a list
digits = [int(char) for char in num_str]

This list comprehension takes every character in the string, converts it to an integer, and builds our digits list—simple and efficient.

Step 2: Initialize variables to track the maximum product #

We'll need two key variables here:

• max_product: To keep track of the largest product we've found so far. Start it at 0 (since all digits are non-negative, this works fine).
• A loop variable (like i) to iterate through the list's indices.

Step 3: Iterate through the list and calculate products #

We need to check every set of 4 adjacent digits. The last valid starting index for a 4-digit group is len(digits) - 4 (since starting at len(digits)-3 would only give us 3 digits). For each starting index i, we grab the slice digits[i:i+4] (this gives us the 4 adjacent digits starting at i), calculate their product, and update max_product if the current product is larger.

Here's the code for this part:

import math

max_product = 0
# Loop through every valid starting index
for i in range(len(digits) - 3):
    # Get the 4 adjacent digits using list slicing
    current_group = digits[i:i+4]
    # Calculate the product of the group
    current_product = math.prod(current_group)
    # Update max_product if current is bigger
    if current_product > max_product:
        max_product = current_product

print(f"The largest product of 4 adjacent digits is: {max_product}")

If you're using a Python version older than 3.8 (where math.prod was introduced), you can calculate the product manually with a loop:

current_product = 1
for num in current_group:
    current_product *= num

Why lists work here #

• Index access & slicing: Lists let us easily grab adjacent elements with slicing (digits[i:i+4]), which is way cleaner than dealing with string indices directly (since we'd have to convert each character to int every time).
• Readability: Using a list of integers makes the code intuitive—anyone reading it can immediately tell we're working with numeric values, not string characters.
• Flexibility: Even though we don't modify the list here, lists are mutable if we ever needed to adjust digits later for edge cases.

Quick note on edge cases #

If the number string contains zeros, that's okay—our code will just calculate the product as zero, and since we're tracking the maximum, it'll ignore those if there's a larger product elsewhere. If all groups include a zero, the max product will correctly be zero.

内容的提问来源于stack exchange，提问作者Durian Jaykin