Leetcode 1248
问题描述
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.
例子
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
方法一
** Solution Java **
** 9ms, beats 87.03% **
** 53MB, beats 100.00% **
class Solution {
public int numberOfSubarrays(int[] nums, int k) {
for (int i = 0; i < nums.length; ++i)
nums[i] %= 2;
return atMost(nums, k) - atMost(nums, k - 1);
}
private int atMost(int[] nums, int k) {
if (k < 0) return 0;
int n = nums.length, res = 0;
for (int i = 0, j = 0; j < n; ++j) {
k -= nums[j];
while (k < 0)
k += nums[i++];
res += j - i + 1;
}
return res;
}
}
方法二
** Solution Java **
** 9ms, beats 87.03% **
** 52.6MB, beats 100.00% **
class Solution {
public int numberOfSubarrays(int[] nums, int k) {
int n = nums.length, res = 0, count = 0;
for (int i = 0, j = 0; j < n; ++j) {
if (nums[j] % 2 == 1) {
--k;
count = 0;
}
while (k == 0) {
k += nums[i++] % 2;
++count;
}
res += count;
}
return res;
}
}