LeetCode | Evaluate Reverse Polish Notation

The algorithm for evaluating any postfix expression is fairly straightforward:

While there are input tokens left

• • Read the next token from input.
  • If the token is a value
    • Push it onto the stack.
  • Otherwise, the token is an operator (operator here includes both operators and functions).
    • It is known a priori that the operator takes n arguments.
    • If there are fewer than n values on the stack
      • (Error) The user has not input sufficient values in the expression.
    • Else, Pop the top n values from the stack.
    • Evaluate the operator, with the values as arguments.
    • Push the returned results, if any, back onto the stack.
• If there is only one value in the stack
  • That value is the result of the calculation.
• Otherwise, there are more values in the stack
  • (Error) The user input has too many values.

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LeetCode | Evaluate Reverse Polish Notation

原文：http://www.cnblogs.com/linyx/p/3656406.html