Given an array of integers arr and two integers k and threshold, return the number of sub-arrays of size k and average greater than or equal to threshold.
Example 1:
Input: arr = [2,2,2,2,5,5,5,8], k = 3, threshold = 4
Output: 3
Explanation: Sub-arrays [2,5,5],[5,5,5] and [5,5,8] have averages 4, 5 and 6 respectively. All other sub-arrays of size 3 have averages less than 4 (the threshold).
Example 2:
Input: arr = [11,13,17,23,29,31,7,5,2,3], k = 3, threshold = 5
Output: 6
Explanation: The first 6 sub-arrays of size 3 have averages greater than 5. Note that averages are not integers.
Constraints:
1 <= arr.length <= 105
1 <= arr[i] <= 104
1 <= k <= arr.length
0 <= threshold <= 104
大小為 K 且平均值大於等於閾值的子陣列數目。
給你一個整數陣列 arr 和兩個整數 k 和 threshold 。請你返回長度為 k 且平均值大於等於 threshold 的子陣列數目。
思路
這道題是一道視窗尺寸固定的滑動視窗題。注意儘量不要在中間過程求平均值因為會涉及到精度問題。在過程中我們可以只求數字的 sum，不求平均值，到最後再計算平均值。
複雜度
時間O(n)
空間O(1)
程式碼
Java實現
class Solution {
public int numOfSubarrays(int[] arr, int k, int threshold) {
int n = arr.length;
int sum = 0;
for (int i = 0; i < k; i++) {
sum += arr[i];
}
int res = 0;
if (sum >= threshold * k) {
res++;
}
for (int i = k; i < n; i++) {
sum += arr[i];
sum -= arr[i - k];
if (sum >= threshold * k) {
res++;
}
}
return res;
}
}