my solution

src/main/java/Solution.java

@@ -1,35 +1,42 @@
 import java.util.*;
-import java.util.function.BiPredicate;
 
+/**
+ * Template code to help you parse the standard input 
+ * according to the problem statement.
+ **/
 class Solution {
 	
-    // best readable version, also without dark ASCII code tricks
+	public static void main( String[] args ) {
-    private static final BiPredicate<Integer, Integer> BRACKETS_MATCH = ( c1, c2 ) -> ( c1 != null && c2 != null )
+		Scanner in = new Scanner( System.in );
-            && (( c1 == '(' && c2 == ')' ) || ( c1 == '[' && c2 == ']' ) || ( c1 == '{' && c2 == '}' ));
+		// read values with in.next...() methods
+		String input = in.nextLine();
+		// code your solution here
+		boolean output = isInputWellFormed(input);
+		// Write result with System.out.println()
+		System.out.println( output );
+	}
 
-    // code your solution here
+	private static boolean isInputWellFormed(String input) {
-    private static boolean checkNextChar( Deque<Integer> stack, Iterator<Integer> iter ) {
+		HashMap<Character, Character> validPairs = new HashMap<>();
-        if ( ! iter.hasNext() ) return stack.isEmpty();
+		validPairs.put('{', '}');
+		validPairs.put('(', ')');
+		validPairs.put('[', ']');
 
-        int c = iter.next();
+		Deque<Character> unmatchedChars = new ArrayDeque<>();
-        if ( BRACKETS_MATCH.test( stack.peek(), c )) {
-            stack.pop();
-        }
-        else {
-            stack.push( c );
-        }
 
-        return checkNextChar( stack, iter );
+		for (int i = 0; i < input.length(); i++) {
-    }
+			char currentChar = input.charAt(i);
 
-    public static void main( String[] args ) {
+			if (validPairs.keySet().contains(currentChar)) {
-        // hint: read values via Scanner methods
+				unmatchedChars.push(currentChar); // Add only opening ({[ to the unmatchedChars.
-        var inputLine = new Scanner( System.in ).nextLine();
+			} else if (validPairs.values().contains(currentChar)) {
-        
+				if (!unmatchedChars.isEmpty() && validPairs.get(unmatchedChars.peekFirst()) == currentChar) {
-        var stack = new ArrayDeque<Integer>( inputLine.length() );
+					unmatchedChars.pop(); // Match found, empty the unmatchedChars.
-        var iter  = inputLine.chars().iterator();
+				} else {
-        
+					return false;
-        // Write result with System.out.println()
+				}
-        System.out.println( checkNextChar( stack, iter ) );
+			}
-    }
+		}
+		return unmatchedChars.isEmpty();
+	}
 }