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 a nut to see which one is bigger/smaller.**Examples: **

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

Another 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 below post.

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

In this post, hashmap based approach is discussed.

- Traverse the nuts array and create a hashmap
- Traverse the bolts array and search for it in hashmap.
- If it is found in the hashmap of nuts then this means bolts exist for that nut.

## C++

`// 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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## Python3

`# Python3 program to implement ` `# above approach` `# Hashmap based solution to ` `# solve` `# Function to match nuts and ` `# bolts` `def` `nutboltmatch(nuts, ` ` ` `bolts, n):` ` ` `hash1 ` `=` `{}` ` ` `# creating a hashmap ` ` ` `# for nuts` ` ` `for` `i ` `in` `range` `(n):` ` ` `hash1[nuts[i]] ` `=` `i` ` ` `# searching for nuts for ` ` ` `# each bolt in hash map` ` ` `for` `i ` `in` `range` `(n):` ` ` `if` `(bolts[i] ` `in` `hash1):` ` ` `nuts[i] ` `=` `bolts[i]` ` ` `# Print the result` ` ` `print` `(` `"matched nuts and bolts are-"` `)` ` ` `for` `i ` `in` `range` `(n):` ` ` `print` `(nuts[i], ` ` ` `end ` `=` `" "` `)` ` ` `print` `()` ` ` `for` `i ` `in` `range` `(n):` ` ` `print` `(bolts[i], ` ` ` `end ` `=` `" "` `)` `# Driver code` `if` `__name__ ` `=` `=` `"__main__"` `:` ` ` `nuts ` `=` `[` `'@'` `, ` `'#'` `, ` `'$'` `,` ` ` `'%'` `, ` `'^'` `, ` `'&'` `]` ` ` `bolts ` `=` `[` `'$'` `, ` `'%'` `, ` `'&'` `,` ` ` `'^'` `, ` `'@'` `, ` `'#'` `]` ` ` `n ` `=` `len` `(nuts)` ` ` `nutboltmatch(nuts, bolts, n)` `# This code is contributed by Chitranayal` |

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**Output: **

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

The 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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