⭐️⭐️⭐️
# 題目敘述
Given a binary array nums and an integer goal , return the number of non-empty subarrays with a sum goal .
A subarray is a contiguous part of the array.
# Example 1
Input: nums = [1,0,1,0,1], goal = 2
Output: 4
Explanation: The 4 subarrays are bolded and underlined below:
[1,0,1,0,1]
[1,0,1,0,1]
[1,0,1,0,1]
[1,0,1,0,1]
# Example 2
Input: nums = [0,0,0,0,0], goal = 0
Output: 15
# 解題思路
# Solution
import java.util.HashMap; | |
import java.util.Map; | |
class Solution { | |
public int numSubarraysWithSum(int[] nums, int goal) { | |
int n = nums.length; | |
int[] prefixSum = new int[n + 1]; | |
for (int i = 0; i < n; i++) { | |
prefixSum[i + 1] = prefixSum[i] + nums[i]; | |
} | |
Map<Integer, Integer> count = new HashMap<>(); | |
int ans = 0; | |
for (int i = 0; i < n + 1; i++) { | |
ans += count.getOrDefault(prefixSum[i] - goal, 0); | |
count.put(prefixSum[i], count.getOrDefault(prefixSum[i], 0) + 1); | |
} | |
return ans; | |
} | |
} |
單字
** **
!! !!
片語 & 搭配詞
!! !!
