Given an array of integers nums and an integer k. A continuous 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 <= 500001 <= nums[i] <= 10^51 <= k <= nums.lengthstruct Solution;
impl Solution {
fn number_of_subarrays(nums: Vec<i32>, k: i32) -> i32 {
let n = nums.len();
let mut count = vec![0; n + 1];
let k = k as usize;
count[0] = 1;
let mut prev = 0;
let mut res = 0;
for i in 0..n {
if nums[i] % 2 == 1 {
prev += 1;
}
count[prev] += 1;
if prev >= k {
res += count[prev - k];
}
}
res as i32
}
}
#[test]
fn test() {
let nums = vec![1, 1, 2, 1, 1];
let k = 3;
let res = 2;
assert_eq!(Solution::number_of_subarrays(nums, k), res);
let nums = vec![2, 4, 6];
let k = 1;
let res = 0;
assert_eq!(Solution::number_of_subarrays(nums, k), res);
let nums = vec![2, 2, 2, 1, 2, 2, 1, 2, 2, 2];
let k = 2;
let res = 16;
assert_eq!(Solution::number_of_subarrays(nums, k), res);
}