| class Set: | |
| def __init__(self): | |
| self.elts = {} | |
| def add(self, elt): | |
| self.elts[elt] = elt | |
| def items(self): | |
| return self.elts.keys() | |
| def has_elt(self, elt): | |
| return self.elts.has_key(elt) | |
| class Stack: | |
| def __init__(self): | |
| self.stack = [] | |
| self.pop = self.stack.pop | |
| def push(self, elt): | |
| self.stack.append(elt) | |
| def top(self): | |
| return self.stack[-1] |