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Provided Code

public class Delimiters
{
    private String openDel;
    private String closeDel;
        public Delimiters(String open, String close) {
        openDel = open; closeDel = close;
    }
    /** Returns ArrayList of only the delimiter tokens (openDel or closeDel) from tokens array. */
        public ArrayList getDelimitersList(String[] tokens) {
        /* part (a) */
    }
    /** Returns true if delimiters are balanced (no excess close before open; equal counts at end). */
        public boolean isBalanced(ArrayList delimiters) {
        /* part (b) */
    }
}

Part A — 4 Points

Write getDelimitersList: loop through tokens, add each token that equals openDel or closeDel to the result ArrayList, and return it.

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Check Answer Clear

public ArrayList getDelimitersList(String[] tokens)
{
    ArrayList result = new ArrayList();
    for (String token : tokens)
    {
        if (token.equals(openDel) || token.equals(closeDel))
        {
            result.add(token);
        }
    }
    return result;
}

Part B — 5 Points

Write isBalanced: return true if (1) at no point do close delimiters exceed open delimiters in count, AND (2) the total open count equals total close count.

Write Your Solution

Check Answer Clear

public boolean isBalanced(ArrayList delimiters)
{
    int openCount = 0;
    int closeCount = 0;
    for (String d : delimiters)
    {
        if (d.equals(openDel))
        {
            openCount++;
        }
        else
        {
            closeCount++;
        }
        if (closeCount > openCount)
        {
            return false;
        }
    }
    return openCount == closeCount;
}

Common Mistakes to Avoid

return openCount == closeCount;  // passes for "  " incorrectly!

if (closeCount > openCount) {
    return false;  // condition 1 inside loop
}
return openCount == closeCount;  // condition 2 after loop

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