CompilersParsers.java

/** https://www.codechef.com/problems/COMPILER #stack */
import java.util.Deque;
import java.util.LinkedList;
import java.util.Scanner;

class CompilersParsers {
  static int calValidPair(String str) {
    Deque<Integer> stack = new LinkedList<>();
    char[] arr = str.toCharArray();
    byte[] resultArr = new byte[arr.length];
    int sumResult = 0;
    for (int i = 0; i < arr.length; i++) {
      if (arr[i] == '<') {
        stack.addLast(i);
      } else { // equals '>'
        if (!stack.isEmpty()) {
          resultArr[i] = 1;
          resultArr[stack.pollLast()] = 1;
          sumResult += 2;
        }
      }
    }
    if (sumResult == 0) {
      return 0;
    }
    int maxLength = 0;
    int count = 0;
    int lastIdx = 0;
    for (int i = 0; i < resultArr.length; i++) {
      if (resultArr[i] == 1) {
        lastIdx = i;
        count += 1;
        if (count > maxLength) {
          maxLength = count;
        }
      } else {
        count = 0;
      }
    }
    // check "><><"
    if (sumResult == 2) {
      if (lastIdx + 1 < str.length()
          && lastIdx >= 2
          && str.substring(lastIdx - 2, lastIdx + 1).equals("><>")) {
        if (arr[lastIdx + 1] == '<') return 0;
      }
    }
    return maxLength;
  }

  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int t = sc.nextInt();
    sc.nextLine();
    String[] arr = new String[t];
    for (int i = 0; i < t; i++) {
      String temp = sc.nextLine();
      arr[i] = temp;
    }
    for (String str : arr) {
      System.out.println(calValidPair(str));
    }
  }
}
/**
 * another way: can apply for character balance Deque<Integer> stack = new LinkedList<>(); char[]
 * arr = str.toCharArray(); int sumResult = 0; int balance = 0; for (int i=0; i < arr.length; i++) {
 * if (arr[i] == '<') { stack.addLast(i); balance++; } else { // equals '>' // balance > 0
 * if(!stack.isEmpty()) { sumResult += 2; balance--; } else { break; } } } // <<> if (balance > 0) {
 * return 0; } return sumResult;
 */