我正在尝试寻找有效解决此问题的算法:
给定一个未排序的数字数组,你需要将其分成几个长度从 a 到 b 的子数组,使得每个子数组中最小数字与最大数字之差的总和最大。必须保留数字的顺序。 例子:
给定一个未排序的数字数组,你需要将其分成几个长度从 a 到 b 的子数组,使得每个子数组中最小数字与最大数字之差的总和最大。必须保留数字的顺序。
例子:
> a = 3, b = 7 > input: [5, 8, 4, 5, 1, 3, 5, 1, 3, 1] > answer: [[5, 8, 4], [5, 1, 3], [5, 1, 3, 1]] (diff sum is 12) > > a = 3, b = 4 > input: [1, 6, 2, 2, 5, 2, 8, 1, 5, 6] > answer: [[1, 6, 2], [2, 5, 2, 8], [1, 5, 6]] (diff sum is 16) > > a = 4, b = 5 > input: [5, 8, 4, 5, 1, 3, 5, 1, 3, 1, 2] > answer: splitting is impossible
到目前为止我想到的唯一解决方案是尝试所有可能的子数组组合。
from collections import deque def partition_array(numbers, min_len, max_len): max_diff_subarray = None queue = deque() for end in range(min_len - 1, max_len): if end < len(numbers): diff = max(numbers[0:end + 1]) - min(numbers[0:end + 1]) queue.append(Subarray(previous=None, start=0, end=end, diff_sum=diff)) while queue: subarray = queue.popleft() if subarray.end == len(numbers) - 1: if max_diff_subarray is None: max_diff_subarray = subarray elif max_diff_subarray.diff_sum < subarray.diff_sum: max_diff_subarray = subarray continue start = subarray.end + 1 for end in range(start + min_len - 1, start + max_len): if end < len(numbers): diff = max(numbers[start:end + 1]) - min(numbers[start:end + 1]) queue.append(Subarray(previous=subarray, start=start, end=end, diff_sum=subarray.diff_sum + diff)) else: break return max_diff_subarray class Subarray: def __init__(self, previous=None, start=0, end=0, diff_sum=0): self.previous = previous self.start = start self.end = end self.diff_sum = diff_sum numbers = [5, 8, 4, 5, 1, 3, 5, 1, 3, 1] a = 3 b = 7 result = partition_array(numbers, a, b) print(result.diff_sum)
还有其他更省时的解决方案吗?
您描述的蛮力方法本质上是对数组的所有可能有效分区进行搜索,将其划分为长度在a和之间的子数组b。虽然它可以工作,但时间复杂度是指数级的,因为您正在探索所有可能的分区,而这对于大型输入数组来说可能会变得非常慢。
a
b
我们可以使用动态规划(DP)来改进算法,以避免重复计算并以更高效的方式解决问题。
我们可以使用动态规划来更高效地解决这个问题,而不是穷尽地尝试所有可能的子数组组合,方法是跟踪数组中每个位置可以形成的最佳子数组。这样,我们只需计算一次每个子数组的贡献,就可以逐步构建解决方案。
dp[i]
numbers[0:i]
i
b``i
dp[0] = 0
j``a``b
dp[len(numbers)]
import numpy as np def partition_array(numbers, min_len, max_len): n = len(numbers) # dp[i] will store the maximum sum of differences up to index i dp = [-float('inf')] * (n + 1) dp[0] = 0 # No subarray, so sum of differences is 0 # To compute max and min efficiently for each possible subarray for i in range(1, n + 1): # Try to form subarrays of length between min_len and max_len for length in range(min_len, max_len + 1): if i - length >= 0: subarray = numbers[i - length:i] diff = max(subarray) - min(subarray) dp[i] = max(dp[i], dp[i - length] + diff) if dp[n] < 0: return "splitting is impossible" return dp[n] # Example usage numbers = [5, 8, 4, 5, 1, 3, 5, 1, 3, 1] a = 3 b = 7 result = partition_array(numbers, a, b) print(result) # Output: 12
min_len
max_len
"splitting is impossible"
dp
对于较大的数组来说,这种方法会更快,并且是针对时间和空间进行优化时该问题最著名的算法。