Given an array with n distinct elements, convert the given array to a form where all elements are in range from 0 to n-1. The order of elements is same, i.e., 0 is placed in place of smallest element, 1 is placed for second smallest element, … n-1 is placed for largest element.

Input: arr[] = {10, 40, 20} Output: arr[] = {0, 2, 1} Input: arr[] = {5, 10, 40, 30, 20} Output: arr[] = {0, 1, 4, 3, 2}

We have discussed simple and hashing based solutions.

In this post, a new solution is discussed. The idea is to create a vector of pairs. Every element of pair contains element and index. We sort vector by array values. After sorting, we copy indexes to original array.

`// C++ program to convert an array in reduced` `// form` `#include <bits/stdc++.h>` `using` `namespace` `std;` ` ` `// Converts arr[0..n-1] to reduced form.` `void` `convert(` `int` `arr[], ` `int` `n)` `{` ` ` `// A vector of pairs. Every element of` ` ` `// pair contains array element and its` ` ` `// index` ` ` `vector <pair<` `int` `, ` `int` `> > v;` ` ` ` ` `// Put all elements and their index in` ` ` `// the vector` ` ` `for` `(` `int` `i = 0; i < n; i++)` ` ` `v.push_back(make_pair(arr[i], i));` ` ` ` ` `// Sort the vector by array values` ` ` `sort(v.begin(), v.end());` ` ` ` ` `// Put indexes of modified vector in arr[]` ` ` `for` `(` `int` `i=0; i<n; i++)` ` ` `arr[v[i].second] = i;` `}` ` ` `// Utility function to print an array.` `void` `printArr(` `int` `arr[], ` `int` `n)` `{` ` ` `for` `(` `int` `i=0; i<n; i++)` ` ` `cout << arr[i] << ` `" "` `;` `}` ` ` `// Driver program to test above method` `int` `main()` `{` ` ` `int` `arr[] = {10, 20, 15, 12, 11, 50};` ` ` `int` `n = ` `sizeof` `(arr)/` `sizeof` `(arr[0]);` ` ` ` ` `cout << ` `"Given Array is \n"` `;` ` ` `printArr(arr, n);` ` ` ` ` `convert(arr , n);` ` ` ` ` `cout << ` `"\n\nConverted Array is \n"` `;` ` ` `printArr(arr, n);` ` ` ` ` `return` `0;` `}` |

Output :

Given Array is 10 20 15 12 11 50 Converted Array is 0 4 3 2 1 5

Time Complexity : O(n Log n)

Auxiliary Space : O(n)

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

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