https://github.com/emahtab/permutations

Permutations
https://github.com/emahtab/permutations

leetcode permutations problem-solving recursion

Last synced: about 1 month ago
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Permutations

• Host: GitHub
• URL: https://github.com/emahtab/permutations
• Owner: eMahtab
• Created: 2019-11-04T01:24:28.000Z (about 5 years ago)
• Default Branch: master
• Last Pushed: 2024-10-27T09:52:04.000Z (2 months ago)
• Last Synced: 2024-10-27T11:05:49.366Z (2 months ago)
• Topics: leetcode, permutations, problem-solving, recursion
• Language: Java
• Homepage:
• Size: 56.6 KB
• Stars: 1
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# Permutations

## https://leetcode.com/problems/permutations

Given a collection of **distinct** integers, return all possible permutations.

```

Example:

Input: [1,2,3]

Output:

[

  [1,2,3],

  [1,3,2],

  [2,1,3],

  [2,3,1],

  [3,1,2],

  [3,2,1]

]

```

![Array Permutations](array-permutations.JPG?raw=true "Array Permutations")

# Implementation : Time = O(n * n!)

```java

class Solution {

    public List> permute(int[] nums) {

    List> result = new ArrayList<>();

    permute(result, new ArrayList(), nums);

    return result;

  }

  private void permute(List> result, List permutation, int[] nums) {

      if(nums.length == 0){

        result.add(permutation);

        return;

      }

      for(int i=0; i < nums.length; i++){

    	 List runningPermutation = new ArrayList(permutation);

    	 runningPermutation.add(nums[i]);

         permute(result, runningPermutation, subArray(nums, i));

      }

  }

    

  private int[] subArray(int[] input, int skipIndex) {

      int subArraySize = input.length - 1;

      int[] subArray = new int[subArraySize];

      int index = 0;

      for(int i = 0; i < input.length; i++){

          if(i != skipIndex)

               subArray[index++] = input[i];

      }

      return subArray;

  }  

    

}

```

### If we are given a String 

![String Permutations](string-permutations.JPG?raw=true "String Permutations")

```java

public class Permutation {

	public static void main(String[] args) {

		permutations("abc");

	}

	public static void permutations(String str) {

		if (str == null || str.length() == 0) {

			System.out.println("Input string is empty !!");

			return;

		} else {

			permute("", str);

		}

	}

	public static void permute(String prefix, String remaining) {

		if (remaining.length() == 0) {

			System.out.println(prefix);

			return;

		}

		for (int i = 0; i < remaining.length(); i++) {

			String newPrefix = prefix + remaining.charAt(i);

			String newRemaining = remaining.substring(0, i) + remaining.substring(i + 1);

			permute(newPrefix, newRemaining);

		}

	}

}

```