Subarray with sum 0 | GeeksforGeeks | Hashing data structure | Leetcode DSA series | Prefix Sum

This is the video under the series of DATA STRUCTURE & ALGORITHM in a HASHING Playlist. We are going to solve the problem "Subarray with 0 sum" from geeks for geeks which are solved by using unordered_set in c++

Given an array of positive and negative numbers. Find if there is a subarray (of size at least one) with 0 sum.

Input:
5
4 2 -3 1 6

Output:
Yes

Explanation: 2, -3, 1 is the subarray with sum 0.

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[rohitrajput]

00:02 Understanding the importance of the subarray with sum 0 question.
01:28 Finding subarray with sum 0 using hashing
02:47 Understanding memory location in a nutshell
04:15 Creating a function with a loop and 500 silencers for a specific calculation
05:40 Identifying subarrays with sum 0
07:05 Understanding prefix sum and subarrays
08:34 Understanding the concept of subarrays and prefix sum
10:13 Understanding subarrays with sum 0

[maniish-sgh]

Done !!
unordered_set<int> s;
int sum = 0;
for (int i = 0; i < arr.size(); i++) {
sum += arr[i];

if (s.find(sum) != s.end() || sum == 0 )
return true;
else
s.insert(sum);
}
return false;

[AmberSparrow]

Your way of explaining is amazing... thank you so much sir 👏👏

[satyamgupta]

thanks bhaiya for such a good explaination.

[DIVYAGUPTA-wuoy]

you great really
explanation is good.

[rode_atharva]

class Solution{
public:
//Complete this function
//Function to check whether there is a subarray present with 0-sum or not.
bool subArrayExists(int arr[], int n)
{
//Your code here
unordered_set<int>s;
int currsum = 0;
s.insert(0);
for(int i=0; i<n; i++){
currsum += arr[i];
if(s.find(currsum) != s.end()){
return true;
}
s.insert(currsum);
}
return false;
}
};//code ho gaya sir logic sikhane ke bad hua par

[_adityasakpal]

THANK YOU BHAIYA, aapki video dekhnese phele solve hi nahi ho paa raha tha

[memesbyanony]

8:43 pe hash me -1 kese aya, it should be 1 ??

[anweshangoswami]

Thanks a lot....that diagram of presum1==presum2 cleared everything

[supriyadas]

In this example {-3, 4, -3, -1, 1} when u stopped at interator 3 previous array which is (-3, 4, -3) not having the sum 0

[RafaelCostaBraga]

Why is the result false for this list [200, 100, -13589, -4, 13589], and it should be true?

[anujpradhan]

Sir, how initially we compare s.find with s.end as there is no element inserted???

[nutankumari]

Thanks for explaining this prefix sum concept in ease way 😊

[akarshitgupta]

watched 2 time because of variable name prefSum1 and prefSum2... 6:33 .. you said ki "vaule aaya one" .. overall explanation was very good..

[masumali]

bool subArrayExists(int arr[], int n)
{
//Your code here
unordered_map<int, int>mp;
for(int i=1;i<n;i++)
{
arr[i]=arr[i]+arr[i-1];
}
for(int i=0;i<n;i++)
{
mp[arr[i]]++;
}

for(auto it:mp)
{
if(it.first==0)
{
return true;
}
else if(it.second>1)
{
return true;
}
}
return false;
}
};

[champofseas]

//Why this is not working

class Solution{
public:
//Complete this function
//Function to check whether there is a subarray present with 0-sum or not.
bool subArrayExists(int arr[], int n)
{
map <int, int> mp;
mp[0]++;
long long int sum = 0;
for(int i=0;i<n;i++){
sum = sum + arr[i];
mp[sum]++;
if(mp[sum]==2){
return true;
}
}
return false;
}
};