Good evening! Here's our prompt for today.

Write an algorithm that takes an input string like "abc", and prints out all possible permutations of the string. A permutation of a group of elements is defined as one of the n! number possible arrangements the elements can take, where n is the number of elements in the range.

We'd expect the following to hold true, note the permutations printed out:

1String str = "abc";
2permutations(str);
3// abc
4// acb
5// bac
6// bca
7// cba
8// cab

A hint here: break the problem down, and think about what steps are going to be repeated. How would we get from "abc" to "acb"?

Constraints

• The string will only consist of lowercase letters
• Length of the string <= 7
• Expected time complexity : O(n*n!)
• Expected space complexity : O(n*n!)

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​

import static org.junit.Assert.*;

​

import java.util.ArrayList;

import java.util.ArrayList;

import java.util.List;

import org.junit.*;

import org.junit.runner.*;

import org.junit.runner.notification.*;

​

public class MainTest {

​

  public static String[] permutations(String str) {

    // fill in this method

    return "";

  }

​

  // tests

​

  @Test

  public void firstTest() {

    assertEquals(

      this.permutations("abc"),

      new String[] { "abc", "acb", "bac", "bca", "cab", "cba" }

    );

  }

​

  @Test

  public void secondTest() {

    assertEquals(this.permutations("a"), new String[] { "a" });

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