problem-6

readme.md

problem-6

Created with <3 with dartpad.dev.

main.dart

// Check for Balanced Brackets in an expression (well-formedness)
// Input: exp = “[()]{}{[()()]()}” Output: Balanced
// Input: exp = “[(])” Output: Not Balanced

void main() {
  final stringChecker = StringChecker1();
  // final result = stringChecker.isValid("{([])}");  ///true
  // final result = stringChecker.isValid("()[]{}");  ///true
  final result = stringChecker.isValid("(]");         ///false
  print("String is well-formed: $result");
}

class StringChecker1 {
  bool isValid(String expr) {
    if (expr.isEmpty) return true;

    List<String> stack = [];

    for (int i = 0; i < expr.length; i++) {
      final x = expr[i];

      if (x == '(' || x == '[' || x == '{') {
        // add the element in the stack (array)
        stack.add(x);
        continue;
      }

      // If current character is not opening
      // bracket, then it must be closing.
      // So stack (array) cannot be empty at this point.
      if (stack.isEmpty) {
        return false;
      }

      final check;

      switch (x) {
        case ')':
          check = stack.removeLast();
          if (check == '{' || check == '[') return false;
          break;

        case '}':
          check = stack.removeLast();
          if (check == '(' || check == '[') return false;
          break;

        case ']':
          check = stack.removeLast();
          if (check == '(' || check == '{') return false;
          break;
      }
    }

    // Check Empty Stack(array)
    return (stack.isEmpty);
  }
}

class StringChecker2 {
  bool isValid(String expr) {
    if (expr.isEmpty) return true;

    // map of parenthesis that we are checking  basically
    Map<String, String> parenthesis = <String, String>{
      ")": "(",
      "}": "{",
      "]": "[",
    };

    // lis to  save the values inside
    List<String> list = <String>[];

    // for loop to check the every entered item in string
    for (String item in expr.split("")) {
      // checking  if the entered string contain the values that inside are same
      if (parenthesis.containsKey(item)) {
        // if the it's zero and length is less than zero or negative
        // OR the it is not same aas the parenthesis  than we will return false
        if (list.isEmpty || list[list.length - 1] != parenthesis[item]) {
          return false;
        } else {
          // removing the last values
          list.removeLast();
        }
      } else {
        // than adding to the list
        list.add(item);
      }
    }
    // if the entered value is empty than it will be false if not than it
    // it will  be true
    return list.isEmpty;
  }
}

class StringChecker3 {
  bool isValid(String expr) {
    if (expr.isEmpty) return true;

    List<String> stack = <String>[];

    for (var i = 0; i < expr.length; i++) {
      if ('([{'.contains(expr[i])) {
        stack.add(expr[i]);
      } else {
        if (expr[i] == ')' &&
            stack.isNotEmpty &&
            stack[stack.length - 1] == '(') {
          stack.removeLast();
        } else if (expr[i] == ']' &&
            stack.isNotEmpty &&
            stack[stack.length - 1] == '[') {
          stack.removeLast();
        } else if (expr[i] == '}' &&
            stack.isNotEmpty &&
            stack[stack.length - 1] == '{') {
          stack.removeLast();
        } else {
          return false;
        }
      }
    }

    return stack.isEmpty;
  }
}