### Description:

Given an array of integers nums and an integer k, return the total number of continuous subarrays whose sum equals to k.

### Solution:

Time Complexity : O(n)

Space Complexity: O(n)

```
var subarraySum = function(nums, k) {
let count = 0, sum = 0;
const map = new Map();
// Add 0 to map as a sum that we have seen and 1 as its value which will be he amount of times we have seen this sum so far
map.set(0, 1);
for (let i = 0; i < nums.length; i++) {
// Get the current sum
sum += nums[i];
// Increase the count if we have seen a sum that equals sum - k
if (map.has(sum - k))
count += map.get(sum - k);
// Set a new value in the map or increase the amount of times this sum has been seen by 1
map.set(sum, (map.get(sum) || 0) + 1);
}
return count;
};
```

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