Mike John Mike John - 3 months ago 7
Java Question

How to check if a String is balanced?

I want to test if an input String is balanced. It would be balanced if there is a matching opening and closing parenthesis, bracket or brace.

example:
{} balanced
() balanced
[] balanced
If S is balanced so is (S)
If S and T are balanced so is ST


public static boolean isBalanced(String in)
{
Stack st = new Stack();

for(char chr : in.toCharArray())
{
if(chr == '{')
st.push(chr);

}

return false;
}


I'm having problems choosing what to do. Should I put every opening or closing parenthesis, bracket, or brace in a stack then pop them out? If I pop them out, how does that really help me?

Answer

1) For every opening bracket: { [ ( push it to the stack.

2) For every closing bracket: } ] ) pop from the stack and check whether the type of bracket matches. If not return false;

i.e. current symbol in String is } and if poped from stack is anything else from { then return false immediately.

3) If end of line and stack is not empty, return false, otherwise true.