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# 560. Subarray Sum Equals K

## Problem Statement

<br>

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

A subarray is a contiguous **non-empty** sequence of elements within an array.

&#x20;

**Example 1:**

<pre><code><strong>Input: nums = [1,1,1], k = 2
</strong><strong>Output: 2
</strong></code></pre>

**Example 2:**

<pre><code><strong>Input: nums = [1,2,3], k = 3
</strong><strong>Output: 2
</strong></code></pre>

&#x20;

**Constraints:**

* `1 <= nums.length <= 2 * 104`
* `-1000 <= nums[i] <= 1000`
* `-107 <= k <= 107`

## Intuition

```
Approach:

The thing is we maintain a prefix sum kind to track the subarrays

eg
1 2 3 arr
1 3 6 pre

Let k=3 sum required

Now
1 2 3
1 3 6

We can see that
)1 2) 3
This gives us the sum 
also

1 2 ) 3 )
this gives 

Also store the sum in map regularly 
Edge case

1) 0) 1 0 1
1  1  2 2 3
Hence we keep track of such 1->2 and then when we encounter 3 - 2 = 1
We take ones count = 2 and add to ans
Sum = 2
1
```

### Links

<https://leetcode.com/problems/subarray-sum-equals-k/description/>

### Video Links

### Approach 1:

```
```

{% code title="C++" lineNumbers="true" %}

```cpp
class Solution {
public:
    int subarraySum(vector<int>& nums, int k) {
        unordered_map<int,int> mp;
        int sum=0, ans=0;
        mp[0] = 1;

        for(int i=0; i<nums.size(); i++){
            sum += nums[i];
            
            if(mp[sum-k]){
                ans += mp[sum-k];
            }

            mp[sum]++;
        }

        return ans;
    }
};
```

{% endcode %}

### Approach 2:

```
```

{% code title="C++" lineNumbers="true" %}

```cpp
```

{% endcode %}

### Approach 3:

```
```

{% code title="C++" lineNumbers="true" %}

```cpp
```

{% endcode %}

### Approach 4:

```
```

{% code title="C++" lineNumbers="true" %}

```cpp
```

{% endcode %}

### Similar Problems

###