930.md

930. Binary Subarrays With Sum

Solution 1 (time O(n), space O(n))

class Solution {
public:
    int numSubarraysWithSum(vector<int>& nums, int goal) {
        unordered_map<int, int> d;
        d[0] = 1;
        int ans = 0;
        int cur_sum = 0;
        for (int i = 0; i < nums.size(); i++) {
            cur_sum += nums[i];
            ans += d[cur_sum - goal];
            d[cur_sum] += 1;
        }
        return ans;
    }
};