import java.util.Stack;

/*

public class Solution {

public int evalRPN(String[] tokens) {

Stack<Integer> stack = new Stack<>();

for (String token : tokens) {

if (isOperator(token)) {

int b = stack.pop();

int a = stack.pop();

int result = applyOperation(a, b, token);

stack.push(result);

} else {

stack.push(Integer.parseInt(token));

}

}

return stack.pop();

}

private boolean isOperator(String token) {

return token.equals("+") || token.equals("-") || token.equals("*") || token.equals("/");

}

private int applyOperation(int a, int b, String op) {

switch(op) {

case "+": return a + b;

case "-": return a - b;

case "*": return a * b;

case "/": return a / b; // Integer division

default: throw new IllegalArgumentException("Invalid operator: " + op);

}

}

public static void main(String[] args) {

Solution sol = new Solution();

String[] tokens = {"2","1","+","3","*"}; // Example

System.out.println(sol.evalRPN(tokens)); // Output: 9

}

}

*/ //1209 leetcode

class Solution {

public String removeDuplicates(String s, int k) {

// Stack stores character and its frequency

Stack<int[]> stack = new Stack<>();

for (char ch : s.toCharArray()) {

if (!stack.isEmpty() && stack.peek()[0] == ch) {

stack.peek()[1]++;

if (stack.peek()[1] == k) {

stack.pop(); // remove k duplicates

}

} else {

stack.push(new int[]{ch, 1});

}

}

// Build result

StringBuilder sb = new StringBuilder();

for (int[] pair : stack) {

char c = (char) pair[0];

int count = pair[1];

while (count-- > 0) {

sb.append(c);

}

}

return sb.toString();

}

}