Use a stack to return a list containing all permutations of a given string. Hint

Question

Use a stack to return a list containing all permutations of a given string. Hint: Suppose you want to find all permutations of the string leaf. Push the string +leaf on the stack. While the stack is not empty Pop off the top of the stack. If that string ends in a + (such as fale+) Remove the + and add the string to the list of permutations. Else Remove each letter in turn from the right of the +. Insert it just before the +. Push the resulting string on the stack. Implement in Java a countOfPermutations method with the following signature: public List countOfPermutations(String word);

Explanation / Answer

import java.util.*;

public class permutations {

public List<String> countOfPermutations(String word) {
List<String> permList = new ArrayList<String>();
Stack<String> myStack = new Stack<String>();
myStack.push(word);
while (!myStack.empty()) {
myStack.pop();
if (word.endsWith("+")) {
permList.add(word.substring(0, word.length() - 1));
} else {
}
}

return permList;
}

}

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