Leetcode 227 Basic Calculator II

1. Description of the problem

Gives an expression of the genetic string type that evaluates the value of an expression. The expression contains only + 、-、 *,/, and spaces.
　　

2. Methods and Ideas

This problem is similar to basic Calculator I, except that the left and right brackets are replaced with the multiplication symbol. The basic practice is to first turn to the form of a suffix expression and then perform the calculation.
Suffix expressions are vector<long> postfix stored in the structure, for convenience, operators and operands are stored in the postfix vector, in order to differentiate, the operands are in the form of negative numbers, and when the calculation becomes a positive number.
　　

classSolution { Public: vector<long>Convert2postfix (Const string&s) { Stack<char>Op vector<long>PostfixintTMP =0, Isprenum =0; for(inti =0; I < s.length (); i++) {Switch(S[i]) { Case "':Continue; Case ' * ': Case '/': while(!op.empty () && (op.top () = =' * '|| Op.top () = ='/') {Postfix.push_back (Op.top ());                Op.pop (); } op.push (S[i]); Break; Case ' + ': Case '-': while(!op.empty ())                    {Postfix.push_back (Op.top ());                Op.pop (); } op.push (S[i]); Break;default:if(isprenum) tmp = tmp*Ten+ S[i]-' 0 ';Else{tmp = S[i]-' 0 '; Isprenum =1; }if(i+1==s.length () | | (I < S.length () && (s[i+1] >' 9 '|| s[i+1] <' 0 ')) {postfix.push_back (-tmp); Isprenum =0; }            }        } while(!op.empty ())            {Postfix.push_back (Op.top ());        Op.pop (); }returnPostfix }intCalculatestrings) { vector<long>Postfix = Convert2postfix (s);if(postfix.size () = =0)return 0; Stack<long>StLongb; for(inti =0; I < postfix.size (); i++) {Switch(Postfix[i]) { Case ' + ': a = St.top (); St.pop ();                b = St.top (); St.pop (); St.push (B+a); Break; Case '-': a = St.top (); St.pop ();                b = St.top (); St.pop (); St.push (B-A); Break; Case ' * ': a = St.top (); St.pop ();                b = St.top (); St.pop (); St.push (b*a); Break; Case '/': a = St.top (); St.pop (); b = St.top (); St.pop ();if(A = =0)return 0; St.push (b/a); Break;default: St.push (-postfix[i]); }        }returnSt.top (); }};

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Leetcode 227 Basic Calculator II