Postfix Expressions
From charlesreid1
About
Postfix expressions:
- expressions in which the operation being specified occurs after the two operands, in a nested way
Example: each postfix expression evaluates to 9.
5 4 +
2 7 * 4 1 + -
1 1 + 1 1 + + 1 1 + 1 1 + + +
Stacks
Postfix expressions can be evaluated by pushing the expressions onto a stack, where the stack deals with expressions. Expressions can consist of a single node (a number), or two expressions and an operator (making the expression definition recursive - like a tree).
In terms of stacks, we can push digits onto the stack UNTIL we reach a symbol, then apply the symbol to the next two expressions on the stack, turn the result into an expression, and push the result expression onto the stack.