---
title: '560. Subarray Sum Equals K'
description: Given an array of integers nums and an integer k, return the total number of subarrays whose sum equals to k
icon: dot
topics:
  - { name: "Array", slug: "array" }
  - { name: "Hash Table", slug: "hash-table" }
  - { name: "Prefix Sum", slug: "prefix-sum" }
video: "fFVZt-6sgyo"
issue: "https://github.com/prdlk/leetcode/issues/38"
companies:
  - { name: "Meta", period: "Thirty Days", frequency: 63.8 }
  - { name: "Google", period: "Thirty Days", frequency: 50.2 }
  - { name: "Visa", period: "Three Months", frequency: 80.9 }
  - { name: "Bloomberg", period: "Three Months", frequency: 74.8 }
  - { name: "Salesforce", period: "Three Months", frequency: 64.7 }
  - { name: "Amazon", period: "Three Months", frequency: 57.1 }
  - { name: "Microsoft", period: "Three Months", frequency: 48.3 }
  - { name: "Accenture", period: "Six Months", frequency: 100 }
  - { name: "IBM", period: "Six Months", frequency: 94.5 }
  - { name: "Infosys", period: "Six Months", frequency: 76.3 }
  - { name: "Apple", period: "Six Months", frequency: 74.7 }
  - { name: "josh technology", period: "Six Months", frequency: 74 }
  - { name: "Walmart Labs", period: "Six Months", frequency: 70.5 }
  - { name: "Yandex", period: "Six Months", frequency: 69.2 }
sidebar:
  label: 'Subarray Sum Equals K'
  badge: 'Medium'
---

### Example 1:
- Input: `nums = [1,1,1], k = 2`
- Output: `2`

### Example 2:
- Input: `nums = [1,2,3], k = 3`
- Output: `2`

### Constraints:

- `1 <= nums.length <= 2 * 10^4`
- `-1000 <= nums[i] <= 1000`
- `-10^7 <= k <= 10^7`

## Approach

```mermaid
flowchart TD
  S(["subarraySum(nums, k)"]) --> I["map = {0: 1} — the empty prefix; sum = 0, count = 0"]
  I --> L{"more n in nums?"}
  L -- no --> E(["return count"])
  L -- yes --> A["sum += n"]
  A --> Q{"map has sum - k?"}
  Q -- yes --> C["count += map.get(sum - k) — every earlier prefix that closes a window"]
  Q -- no --> W["map.set(sum, count of sum + 1)"]
  C --> W
  W --> L
```

## Solution

```js
/**
 * @param {number[]} nums
 * @param {number} k
 * @return {number}
 */
var subarraySum = function(nums, k) {
  const map = new Map();
  map.set(0, 1);

  let sum = 0;
  let count = 0;

  for (let n of nums){
    sum += n;

    if(map.has(sum - k)){
      count += map.get(sum - k);
    }

    map.set(sum, (map.get(sum) || 0) + 1);
  }
  return count
};
```