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// https://leetcode.com/problems/make-the-string-great

// T: O(N)

// S: O(N)

import java.util.Stack;

public class MakeTheStringGreat {

public String makeGood(String s) {

final Stack<Character> characters = new Stack<>();

for (int index = 0 ; index < s.length() ; index++) {

char c = s.charAt(index);

if (!characters.isEmpty() && c == inverse(characters.peek())) {

characters.pop();

} else characters.push(c);

}

return toStringBuilder(characters).reverse().toString();

}

private StringBuilder toStringBuilder(Stack<Character> stack) {

StringBuilder result = new StringBuilder();

while (!stack.isEmpty()) result.append(stack.pop());

return result;

}

private char inverse(char c) {

return Character.isUpperCase(c) ? Character.toLowerCase(c) : Character.toUpperCase(c);

}