Python3 程序查找具有最小平均数的子数组
给定一个大小为 n 的数组 arr[] 和整数 k,使得 k <= n。
例子 :
Input: arr[] = {3, 7, 90, 20, 10, 50, 40}, k = 3
Output: Subarray between indexes 3 and 5
The subarray {20, 10, 50} has the least average
among all subarrays of size 3.
Input: arr[] = {3, 7, 5, 20, -10, 0, 12}, k = 2
Output: Subarray between [4, 5] has minimum average
我们强烈建议您单击此处并进行练习,然后再继续使用解决方案。
一个简单的解决方案是将每个元素视为大小为 k 的子数组的开始,并计算从该元素开始的子数组的总和。该解决方案的时间复杂度为 O(nk)。
一个有效的解决方案是在 O(n) 时间和 O(1) 额外空间内解决上述问题。这个想法是使用大小为 k 的滑动窗口。跟踪当前 k 个元素的总和。要计算当前窗口的总和,请删除前一个窗口的第一个元素并添加当前元素(当前窗口的最后一个元素)。
1) Initialize res_index = 0 // Beginning of result index
2) Find sum of first k elements. Let this sum be 'curr_sum'
3) Initialize min_sum = sum
4) Iterate from (k+1)'th to n'th element, do following
for every element arr[i]
a) curr_sum = curr_sum + arr[i] - arr[i-k]
b) If curr_sum < min_sum
res_index = (i-k+1)
5) Print res_index and res_index+k-1 as beginning and ending
indexes of resultant subarray.
下面是上述算法的实现。
Python3
# Python3 program to find
# minimum average subarray
# Prints beginning and ending
# indexes of subarray of size k
# with minimum average
def findMinAvgSubarray(arr, n, k):
# k must be smaller than or equal to n
if (n < k): return 0
# Initialize beginning index of result
res_index = 0
# Compute sum of first subarray of size k
curr_sum = 0
for i in range(k):
curr_sum += arr[i]
# Initialize minimum sum as current sum
min_sum = curr_sum
# Traverse from (k + 1)'th
# element to n'th element
for i in range(k, n):
# Add current item and remove first
# item of previous subarray
curr_sum += arr[i] - arr[i-k]
# Update result if needed
if (curr_sum < min_sum):
min_sum = curr_sum
res_index = (i - k + 1)
print("Subarray between [", res_index,
", ", (res_index + k - 1),
"] has minimum average")
# Driver Code
arr = [3, 7, 90, 20, 10, 50, 40]
k = 3 # Subarray size
n = len(arr)
findMinAvgSubarray(arr, n, k)
# This code is contributed by Anant Agarwal.
输出:
Subarray between [3, 5] has minimum average
时间复杂度:O(n)
辅助空间:O(1)
有关更多详细信息,请参阅有关查找具有最低平均值的子数组的完整文章!