20.png
public boolean isValid(String s) {
Stack<Character> stack = new Stack<Character>();
for( int i = 0 ; i < s.length() ; i ++ )
if( s.charAt(i) == '(' || s.charAt(i) == '{' || s.charAt(i) == '[')
stack.push(s.charAt(i));
else{
if( stack.size() == 0 )
return false;
Character c = stack.pop();
Character match;
if( s.charAt(i) == ')' )
match = '(';
else if( s.charAt(i) == ']' )
match = '[';
else{
assert s.charAt(i) == '}';
match = '{';
}
if(c != match)
return false;
}
if( stack.size() != 0 )
return false;
return true;
}
