Lintcode:expression Evaluation (Basic Calculator III)

return Final  This   This question in a real interview?  2*6-(23+7)/(1+2), input is[  "2", "*", "6", "-", "(",  "+", "+", "7", ")", "/", c11/> ("," 1 "," + "," 2 ",")"],return 2+,-, *,/, (,).

This problem should actually be the basic Calculator III. Reference to the http://blog.csdn.net/nicaishibiantai/article/details/45740649

The idea is that there are two stacks, one stored number and one symbol. If a number is encountered, it is stored directly to the digital stack, and if a symbol is encountered, there are several cases:

1. The current symbol has a higher priority than the previous symbol, such as * above +, then directly into the stack

2. If the current symbol is lower than the previous, then all the existing symbols in the stack must be completed before the current symbol is pushed

3. The current symbol is "(", Direct push

4. The current symbol is ")", it is necessary to all "(" the previous symbol all finished

1  Public classSolution {2     /**3      * @paramExpression:an array of strings;4      * @return: An integer5      */6      Public intevaluateexpression (string[] expression) {7         //Write your code here8stack<integer> integers =NewStack<integer>();9stack<string> Ops =NewStack<string>();Ten         inti = 0; One          while(I <expression.length) { AString cur =Expression[i]; -             if(isOp (cur)) {//Current string was an op -                 if(Cur.equals ("(") ) Ops.push (cur); the                 Else if(Cur.equals (")")) { -                      while(Ops.size () >0 &&!ops.peek (). Equals ("(")) { - Integers.push (Calc (Integers.pop (), Integers.pop (), Ops.pop ())); -                     } + Ops.pop (); -                 } +                 Else{// +,-,*,/ A                      while(Ops.size () >0 &&precede (cur, ops.peek ())) { at Integers.push (Calc (Integers.pop (), Integers.pop (), Ops.pop ())); -                     } - Ops.push (cur); -                 } -             } -             ElseIntegers.push (integer.parseint (cur));//Current String is a integer, push to Integer stack ini++; -         } to          +          while(!Ops.isempty ()) { - Integers.push (Calc (Integers.pop (), Integers.pop (), Ops.pop ())); the         } *         returnIntegers.isempty ()? 0: Integers.pop (); $     }Panax Notoginseng      -      Public BooleanisOp (String input) { the         if(Input.equals ("+") | | input.equals ("-") | | input.equals ("*") +|| Input.equals ("/") | | Input.equals ("(") | | Input.equals (")")) A             return true; the         return false; +     } -      $      Public intCalcintAintB, String op) { $         if(Op.equals ("+"))returnA +b; -         Else if(Op.equals ("-"))returnB-A; -         Else if(Op.equals ("*"))returnA *b; the         Else returnb/A; -     }Wuyi      the      Public Booleanprecede (string A, string b) { -         if(B.equals ("*") | | b.equals ("/"))return true; Wu         if(B.equals ("+") | | b.equals ("-"))) { -             if(A.equals ("*") | | a.equals ("/"))return false; About             Else return true; $         } -         return false//case like (a+b) to the first + number, + and (than should return false -     } -};

Lintcode:expression Evaluation (Basic Calculator III)