> For the complete documentation index, see [llms.txt](https://coding-9.gitbook.io/untitled/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://coding-9.gitbook.io/untitled/array/easy/longest-sub-array-with-sum-k.md).

# Longest Sub-Array with Sum K

## Problem Statement

\
Given an array containing **N** integers and an integer **K**., Your task is to find the length of the longest Sub-Array with the sum of the elements equal to the given value **K**.

 

**Example 1:**\
 

<pre><code><strong>Input :
</strong>A[] = {10, 5, 2, 7, 1, 9}
K = 15
<strong>Output : 4
</strong><strong>Explanation:
</strong><strong>The sub-array is {5, 2, 7, 1}.
</strong></code></pre>

**Example 2:**

<pre><code><strong>Input : 
</strong>A[] = {-1, 2, 3}
K = 6
<strong>Output : 0
</strong><strong>Explanation: 
</strong>There is no such sub-array with sum 6.
</code></pre>

**Your Task:**\
This is a function problem. The input is already taken care of by the driver code. You only need to complete the function **lenOfLongSubarr()** that takes an array **(A)**, sizeOfArray **(n)**,  sum **(K)**&#x61;nd **returns** the required length of the longest Sub-Array. The driver code takes care of the printing.

**Expected Time Complexity:** O(N).\
**Expected Auxiliary Space:** O(N).

&#x20;

**Constraints:**\
1<=N<=105\
-105<=A\[i], K<=105

## Intuition

```
Carry prefix sum
Store each element in map 

And check if Prefix sum - k exists in map
Update length accordingly

"Check out the solution in this: Prefix sum for K=0  and using running sum we calculate the answer

Zero is put in advance to find eg- sum=15 and K=15 then sum-K = 0 ;
To find this difference in hash

As an when we 
index  -1|  0   1   2    3   4   5 
arr[i]   0  |10   5   2   7    1   9
sum   0  | 10 15 17 24 25 34

Everytime we encounter the sum we get last index 
check for eg
at index 4 25-15 10 we fall on last sum

"
```

### Links

<https://practice.geeksforgeeks.org/problems/longest-sub-array-with-sum-k0809/1>

### Video Links

<https://www.youtube.com/watch?v=yDeNqw_dAU0>

### Approach 1:

```
```

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

```cpp
class Solution{
    public:
    int lenOfLongSubarr(int A[],  int N, int K) 
    { 
        map<int,int>mp;
        int sum=0;
        mp[0]=-1;   // for case of -2 1 1
        int l=0;            //prefix sum   -2 -1 0  but to see 0 in hash we have to put it first          
        
        // 10 5  2  7  1  9
        // 10 15 17 24 25 34
        
        for(int i=0;i<N;i++){
            sum+=A[i];
            
            if(mp.find(sum-K)!=mp.end()){
               l=max(l,i-mp[sum-K]);
            }
            
            if(mp.find(sum)==mp.end())
            {
                mp[sum]=i;
            }
            
        }
        
        return l;
        
    } 


};
```

{% 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

###