<p>Given an array of integers <code>nums</code> and an integer <code>k</code>, return <em>the total number of subarrays whose sum equals to</em> <code>k</code>.</p>

<p>A subarray is a contiguous <strong>non-empty</strong> sequence of elements within an array.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> nums = [1,1,1], k = 2
<strong>Output:</strong> 2
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> nums = [1,2,3], k = 3
<strong>Output:</strong> 2
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 2 * 10<sup>4</sup></code></li>
	<li><code>-1000 &lt;= nums[i] &lt;= 1000</code></li>
	<li><code>-10<sup>7</sup> &lt;= k &lt;= 10<sup>7</sup></code></li>
</ul>

#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
static const bool __boost = []() {
	cin.tie(nullptr);
	cout.tie(nullptr);
	return std::ios_base::sync_with_stdio(false);
	}();


const size_t BUFFER_SIZE = 0x6fafffff;
alignas(std::max_align_t) char buffer[BUFFER_SIZE];
size_t buffer_pos = 0;
void* operator new(size_t size) {
	constexpr std::size_t alignment = alignof(std::max_align_t); // Default maximum alignment
	size_t padding = (alignment - (buffer_pos % alignment)) % alignment;
	size_t total_size = size + padding;
	char* aligned_ptr = &buffer[buffer_pos + padding];
	buffer_pos += total_size;
	return aligned_ptr;
}
void operator delete(void* ptr) {
}

// Overload the delete[] operator to do nothing
void operator delete[](void* ptr) {}

#include <execution>
#include <unordered_map>

class Solution {
public:
    int subarraySum(vector<int>& nums, int k) {
        int n = nums.size();

        if (!n)
            return 0;
        else if (n == 1)
            return nums[0] == k ? 1 : 0;

        std::unordered_map<int, int> sums;
        int res = 0, currentSum = 0;
        for (int i = 0; i < n; i++)
        {
            currentSum += nums[i];
            if (currentSum == k)
                ++res;
            if (sums.find(currentSum - k) != sums.end())
                res += sums[currentSum - k];
            sums[currentSum]++;
        }

        return res;
    }
};
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