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Check if a given string is a balanced parenthesis string, recursively

I am having problems with a newbie in java (and generally programming) with the task that we were given. The assignment is divided into 3 parts to check whether a given line has balanced brackets.

The "rules" are as follows:

  • "abcdefksdhgs" - balanced
  • "[{aaa<bb>dd}]<232>" - balanced
  • "[ff{<gg}]<ttt>"- NOT balanced (no close for < )
  • "{<}>" - NOT balanced

The first part of the task was to write a method that gets a char array containing a string and finds a FIRST index (= array cell) containing a bracket, one of the following:

} , { , ] , [ , ( , ) , > , <

This, of course, was easily done:

/**
 * bracketIndex - 1st Method:
 * this method will get a single string (read from the text file),
 * and will find the first index char that is any bracket of the following: },{,],[,(,),>,<
 * @param str1 - the given string.
 * @return index - the first index that contains character that is one of the brackets listed above.
 */
public static int bracketIndex(String str1){
        int index = -1; // default value: didn't find any bracket in the string.
        int i = 0;
        for( i = 0; i < str1.length(); i++ ){
                if(str1.charAt(i) == '}' || str1.charAt(i) == '{' || str1.charAt(i) == ']' || str1.charAt(i) == '[' || str1.charAt(i) == '(' || str1.charAt(i) == ')' || str1.charAt(i) == '>' || str1.charAt(i) == '<'){
                        return index = i;
                }//if
        }//for
        return index;
}//end of bracketIndex

, , , true, char char (: 1st = '<' 2nd = ' > '= true ( false!), 1st ='<'2nd =' e '= false). :

/**
 * checkBracket - 2nd Method:
 *
 * @param firstChar, secondChar - two chars.
 * @return True - if the the two chars are brackets, in which the second char is the closing bracket of the first char
 */
public static boolean checkBracket(char firstChar, char secondChar){
        if (    (firstChar == '(') && (secondChar == ')') ||
                        (firstChar == '[') && (secondChar == ']') ||
                        (firstChar == '{') && (secondChar == '}') ||
                        (firstChar == '<') && (secondChar == '>')   ){
                return true;
        }//if
        return false;
}//end of checkBracket

- RECURSIVE, , "true", , . , 1- 2- , , :

: , 2

. :

  • - true
  • , true ( )
  • - true

, false. , 26 :

/**
 * checkBalance - 3rd Method:
 * will check if a given string is a balanced string.
 * @param str1 - the given string to check.
 * @return true - if the given string is balanced, false - if the given string isn't balanced.
 */
public static boolean checkBalance(String str1){
        boolean ans;
        int a = bracketIndex(str1);
        if ( a == -1 ){
                return ans = true;
        }//if
        if( str1.charAt(a) == '{' ||
                        str1.charAt(a) == '[' ||
                        str1.charAt(a) == '<' ||
                        str1.charAt(a) == '('   ){
                int b = bracketIndex(str1.substring(a))+1 ;
                if( b != 0 ){
                        if( checkBracket ( str1.charAt(a), str1.charAt(b) ) == true ){
                                return ans = true;
                        }//if
                        if( str1.charAt(b) == '{' ||
                                        str1.charAt(b) == '[' ||
                                        str1.charAt(b) == '<' ||
                                        str1.charAt(b) == '('   ){
                                checkBalance(str1.substring(b-1));
                        }//if
                        else{
                                return ans = false;
                        }//else
                }//if
        }//if
        return ans = false;
}//end of checkBalance

, , 26 true.

, , .

+4
5

, , , , :

  • ,
  • , , nerver, , .

, ( ) return true, else false

ALGORITHM ( Java):

public static boolean isBalanced(final String str1, final LinkedList<Character> openedBrackets, final Map<Character, Character> closeToOpen) {
    if ((str1 == null) || str1.isEmpty()) {
        return openedBrackets.isEmpty();
    } else if (closeToOpen.containsValue(str1.charAt(0))) {
        openedBrackets.add(str1.charAt(0));
        return isBalanced(str1.substring(1), openedBrackets, closeToOpen);
    } else if (closeToOpen.containsKey(str1.charAt(0))) {
        if (openedBrackets.getLast() == closeToOpen.get(str1.charAt(0))) {
            openedBrackets.removeLast();
            return isBalanced(str1.substring(1), openedBrackets, closeToOpen);
        } else {
            return false;
        }
    } else {
        return isBalanced(str1.substring(1), openedBrackets, closeToOpen);
    }
}

TEST

public static void main(final String[] args) {
    final Map<Character, Character> closeToOpen = new HashMap<Character, Character>();
    closeToOpen.put('}', '{');
    closeToOpen.put(']', '[');
    closeToOpen.put(')', '(');
    closeToOpen.put('>', '<');

    final String[] testSet = new String[] { "abcdefksdhgs", "[{aaa<bb>dd}]<232>", "[ff{<gg}]<ttt>", "{<}>" };
    for (final String test : testSet) {
        System.out.println(test + "  ->  " + isBalanced(test, new LinkedList<Character>(), closeToOpen));
    }
}

OUTPUT

abcdefksdhgs  ->  true
[{aaa<bb>dd}]<232>  ->  true
[ff{<gg}]<ttt>  ->  false
{<}>  ->  false

, :

import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;
0

- , , , .

-, . , checkBalanced(String str, int start, int end). , checkBalanced(String str) { return checkBalanced(str,0,str.length()-1; }, "" , , .

. , . - , . , , . .

, , checkBalanced , checkBalanced . ( , " " string.length(), , . , , .) , .

0

regexp. : <bb>, ( ) , . :

static Pattern noBrackets = Pattern.compile("^[^\\[\\]{}()<>]*$");
static Pattern p = Pattern.compile("[{(<\\[][^\\[\\]{}()<>]*[})>\\]]");

static boolean balanced(String s) {
    if (s.length() == 0) {
        return true;
    }
    Matcher m = p.matcher(s);
    if (!m.find()) {
        m = noBrackets.matcher(s);
        return m.find();
    }
    boolean e;
    switch (s.charAt(m.start())) {
        case '{':
            e = s.charAt(m.end() - 1) == '}';
            break;
        case '[':
            e = s.charAt(m.end() - 1) == ']';
            break;
        case '(':
            e = s.charAt(m.end() - 1) == ')';
            break;
        case '<':
            e = s.charAt(m.end() - 1) == '>';
            break;
        default:
            return false;
    }
    if (!e) {
        return false;
    }
    return balanced(s.substring(0, m.start()) + s.substring(m.end()));
}

public static void main(String[] args) {
    for (String s : new String[]{
        "abcdefksdhgs",
        "[{aaa<bb>dd}]<232>",
        "[ff{<gg}]<ttt>",
        "{<}>"
    }) {
        System.out.println(s + ":\t" + balanced(s));
    }
}

:

abcdefksdhgs:   true
[{aaa<bb>dd}]<232>: true
[ff{<gg}]<ttt>: false
{<}>:   false
0
//basic code non strack algorithm just started learning java ignore space and time.
/// {[()]}[][]{}
// {[( -a -> }]) -b -> replace a(]}) -> reverse a( }]))-> 
//Split string to substring {[()]}, next [], next [], next{}

public class testbrackets {
    static String stringfirst;
    static String stringsecond;
    static int open = 0;
    public static void main(String[] args) {
        splitstring("(()){}()");
    }
static void splitstring(String str){

    int len = str.length();
    for(int i=0;i<=len-1;i++){
        stringfirst="";
        stringsecond="";
        System.out.println("loop starttttttt");
        char a = str.charAt(i);
    if(a=='{'||a=='['||a=='(')
    {
        open = open+1;
        continue;
    }
    if(a=='}'||a==']'||a==')'){
        if(open==0){
            System.out.println(open+"started with closing brace");
            return;
        }
        String stringfirst=str.substring(i-open, i);
        System.out.println("stringfirst"+stringfirst);
        String stringsecond=str.substring(i, i+open);
        System.out.println("stringsecond"+stringsecond);
        replace(stringfirst, stringsecond);

        }
    i=(i+open)-1;
    open=0;
    System.out.println(i);
    }
    }
    static void replace(String stringfirst, String stringsecond){
        stringfirst = stringfirst.replace('{', '}');
        stringfirst = stringfirst.replace('(', ')');
        stringfirst = stringfirst.replace('[', ']');
        StringBuilder stringfirst1 = new StringBuilder(stringfirst);
        stringfirst = stringfirst1.reverse().toString();
    System.out.println("stringfirst"+stringfirst);
    System.out.println("stringsecond"+stringsecond);
if(stringfirst.equals(stringsecond)){
    System.out.println("pass");
}
    else{
        System.out.println("fail");
        System.exit(0);
        }
    }
}
0

, . :

public boolean isValid(String s) {
    HashMap<Character, Character> closeBracketMap = new HashMap<Character, Character>();
    closeBracketMap.put(')', '(');
    closeBracketMap.put(']', '[');
    closeBracketMap.put('}', '{');
    closeBracketMap.put('>', '<');
    HashSet<Character> openBracketSet = new HashSet<Character>(
        closeBracketMap.values());
    Stack<Character> stack = new Stack<Character>();
    char[] chars = s.toCharArray();
    for (int i = 0; i < chars.length; i++) {
        char cur = chars[i];
        if (openBracketSet.contains(cur)) {
            stack.push(cur);
        } else if (closeBracketMap.keySet().contains(cur)) { // close brackets
            if (stack.isEmpty()) {
                return false;
            }
            if (closeBracketMap.get(cur) != stack.peek()) {
                return false;
            }
            stack.pop();
        }
    }
    return stack.isEmpty();
}
0

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