CODEWITHSUNDEEP
c++data-structures
StrawHat04
StrawHat04

Reputation: 11

Pair within an unsorted Array for a given Sum

Here it is using the unordered_map for the hashtable concept but I am not sure how it is doing so without even inserting item into the key value pair of undered_map.

This is the code for finding the pairs within an unsorted array. Here it is using hashtable concept for everyother element.

void findPair(int arr[],int n,int x)
{
    unordered_map<int,int> umap;
    for(int i=0;i<n;i++)
    {
        int temp=x-arr[i];
        if(umap.find(temp)!=umap.end())
        {
            int count=umap[temp];
            for(int j=0;j<count;j++)
                cout<<arr[i]<<" "<<temp<<"\n";
        }
        umap[arr[i]]++;
    }
}

Can you please give me some insight how it is inserting and why it is incrementing the count of that value?

Upvotes: 0

Views: 108

Answers (1)

Alecto
Alecto

Reputation: 10750

The map counts the number of times each element occurs in the unsorted array. By default, if you write

umap[key]

and key is not in umap, it inserts key into umap with a default value of 0. It then returns a reference to the location where the key was stored in the map.

This means that for a new key given by arr[i], the key is inserted into the map when you call umap[arr[i]], and then that value is incremented so that the map registers a count of 1 for that key.

Upvotes: 1

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