Nuts & Bolts Problem (Lock & Key problem) | Set 2 (Hashmap)

Given a set of n nuts of different sizes and n bolts of different sizes. There is a one-one mapping between nuts and bolts. Match nuts and bolts efficiently.
Constraint: Comparison of a nut to another nut or a bolt to another bolt is not allowed. It means nut can only be compared with bolt and bolt can only be compared with nut to see which one is bigger/smaller.

Examples:

Input : nuts[] = {'@', '#', '$', '%', '^', '&'}
        bolts[] = {'$', '%', '&', '^', '@', '#'}
Output : Matched nuts and bolts are-
        $ % & ^ @ # 
        $ % & ^ @ #  

Other way of asking this problem is, given a box with locks and keys where one lock can be opened by one key in the box. We need to match the pair.

We have discussed a sorting based solution in below post.

Nuts & Bolts Problem (Lock & Key problem) | Set 1

In this post, hashmap based approach is discussed.

  1. Travese the nuts array and create a hashmap
  2. Traverse the bolts array and search for it in hashmap.
  3. If it is found in the hashmap of nuts than this means bolts exist for that nut.
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// Hashmap based solution to solve
#include <bits/stdc++.h>
using namespace std;
  
// function to match nuts and bolts
void nutboltmatch(char nuts[], char bolts[], int n)
{
    unordered_map<char, int> hash;
  
    // creating a hashmap for nuts
    for (int i = 0; i < n; i++)
        hash[nuts[i]] = i;
  
    // searching for nuts for each bolt in hash map
    for (int i = 0; i < n; i++)
        if (hash.find(bolts[i]) != hash.end())
            nuts[i] = bolts[i];
  
    // print the result
    cout << "matched nuts and bolts are-" << endl;
    for (int i = 0; i < n; i++)
        cout << nuts[i] << " ";
    cout << endl;
    for (int i = 0; i < n; i++)
        cout << bolts[i] << " ";
}
  
// Driver code
int main()
{
    char nuts[] = {'@', '#', '$', '%', '^', '&'};
    char bolts[] = {'$', '%', '&', '^', '@', '#'};
    int n = sizeof(nuts) / sizeof(nuts[0]);
    nutboltmatch(nuts, bolts, n);
    return 0;
}

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Output:

matched nuts and bolts are-
$ % & ^ @ # 
$ % & ^ @ # 

Time complexity for this solution is O(n).

This article is contributed by Niteesh kumar. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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