"JAVA" "leetcode" "use stack for back calculation"

Title: evaluate-reverse-polish-notation

Requirements:

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid Operators are+,-, *,/. Each operand is an integer or another expression.

Some examples:

  ["2", "1", "+", "3", "*")--((2 + 1) (3)-9  ["4", "", "5", "/", "+"], 4 + (13/5))

Understand:

The latter calculation, such as (2,1+3*), is (2+1), the principle of using the stack implementation is push (2) into the stack, push (1) into the stack, when the symbol "+" is encountered, a = Pop (), then B = Pop (), the implementation of b+a,

Then the (b+a) and then push into the stack, until the next sign of the arrival of the pop out of the stack to participate in the calculation, until the completion of the calculation of all the characters Entered.

ImportJava.util.*; public classSolution { public intevalrpn (string[] Tokens) {Stack<Integer> stack =NewStack<integer>();  for(inti=0;i<tokens.length;i++){            Try{                intnum =Integer.parseint (tokens[i]);            Stack.push (num); }Catch(Exception E) {intA =Stack.pop (); intb =Stack.pop ();            Stack.push (operate (b,a,tokens[i)); }        }        returnStack.pop (); }              public intOperateintAintb,string Token) {            Switch(token) { case"+":returnA +b;  case"-":returna-b;  case"*":returnA *b;  case"/":                if(b==0)                    return0; Else                    returna/b; default:return0; }        }        }

"JAVA" "leetcode" "use stack for back calculation"