題目描述
Given an array of integers nums and an integer k. A subarray is called nice if there are k odd numbers on it.
Return the number of nice sub-arrays.
Example 1:
Input: nums = [1,1,2,1,1], k = 3
Output: 2
Explanation: The only sub-arrays with 3 odd numbers are [1,1,2,1] and [1,2,1,1].
Example 2:
Input: nums = [2,4,6], k = 1
Output: 0
Explanation: There is no odd numbers in the array.
Example 3:
Input: nums = [2,2,2,1,2,2,1,2,2,2], k = 2
Output: 16
Constraints:
1 <= nums.length <= 50000
1 <= nums[i] <= 10^5
1 <= k <= nums.length
思路
累計當前區間內奇數的個數，等於k個時，左區間增加，統計個數。只有當右區間新覆蓋了奇數時，重新開始當前計數。
代碼
class Solution {
public:
int numberOfSubarrays(vector<int>& nums, int k) {
int n = nums.size();
int res = 0, cnt = 0, cur = 0;
for (int i=0, j=0; i<n; ++i) {
if (nums[i] % 2) cnt++;
if (cnt == k) cur = 0;
while(cnt == k) {
cur++;
if (nums[j] % 2) cnt--;
j++;
}
res += cur;
}
return res;
}
};