Let’s run findPermutation with this addition. If this is true, we can continue, which will essentially skip the current iterative loop and move on to the next. indexOf returns the first index of a character, so if we’ve already run findPermutations for an “a”, for example, the indexOf(“a”) will be different than the index of char, the current, later “a”. There are a lot of different ways to remove superfluous elements, but I chose to use Javascript’s indexOf method to identify if the current character has already been run through our findPermutations method. If (!string || typeof string != "string") If my final solution may return more than one “correct” element (in this case, permutations), I’ll need a place to store them before I return the complete solution.Ģ: Iterate! If I need to find all the ordered combinations of characters in a string, creating a loop to iterate through all the characters in a string seems like a decent place to start. When I see a challenge like this, my first instinct is two do two things:ġ: Make an empty array. So we’ve figured out what a permutation is, and established that (depending on the length of the string) we may be looking for a lot of them. Suddenly, this whole string-manipulation problem seems a bit more intimidating. The whole point of combination locks is that a relatively small amount of numbers can create a large enough number of ordered combinations to prohibit casual opening. However, it does not need to be an existing word, but can simply be a re-arrangement of the characters.Īn example of permutations of something other than a string would be this:įor just three colors, we can have six different permutations, or ordered combinations of those colors.Īnother example of permutations would be a combination lock: A string permutation is similar to an anagram. So every string has a number of permutations into which its characters could be re-arranged. The solution model I explore here utilizes tools and concepts that I find broadly valuable for the solution of algorithmic challenges, and methods that I find intuitive for string manipulation within Javascript.įirst things first: What is a permutation?Ī way, especially one of several possible variations, in which a set or number of things can be ordered or arranged. Note : There is more than one way to solve this problem. Why? While the task of manipulating a string may seem familiar on its surface, actually finding a complete solution requires us to handle some unexpected complexity, which provides the opportunity to utilize a recursive tree and build a bit of familiarity with the master theorem. When I sat down to solve this problem, I found it to be a great algorithm challenge. Given a string, return all permutations of the string. The output will be “abc,acb,bca,bac,cab,cba,” representing all the unique combinations of the characters in the input string.GitHub repo with completed solution code and test suite. The program uses a recursive approach to generate all the possible permutations of the input string “abc” and prints them comma-separated. Finally, it returns the updated string after the swap.Then, it swaps the characters at indices i and j using a temporary variable temp.It converts the string a to a character array ch.The swap method takes a string a and two indices i and j as parameters.After the recursion, the swap method is called again to restore the original order of characters.Then, the merge method is recursively called with the updated string and an incremented lower bound (lb + 1).In each iteration, the swap method is called to swap the characters at the lb and i indices of the string str.Otherwise, a loop runs from the lower bound (lb) to the upper bound (ub).If the lower bound (lb) is equal to the upper bound (ub), it means that a single permutation is obtained, and it is printed followed by a comma. The merge method uses recursion to generate all permutations of the input string.The method is called with the input string str, and the lower bound (lb) is set to 0, and the upper bound (ub) is set to n – 1.The merge method is called to generate all the permutations of the input string.The length of the string n is calculated using the length method.The input string str is initialized with the value “abc.”.The program starts executing from the main method.
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