Leetcode 224. Basic Calculator

Implement a basic calculator to calculate the value of a simple string expression.

String expressions can contain opening parentheses ( , closing parentheses ) , plus + , minus, nonnegative integers, - and spaces   .

Example 1:

Input: "1 + 1" Output: 2

Example 2:

Input: "2-1 + 2" output: 3

Example 3:

Input: "(1+ (4+5+2)-3) + (6+8)" Output: 23

Description

• You can assume that the given expression is valid.
• Please do not use the built-in library functions eval .

The code to write at the beginning is as follows, too redundant:

classSolution { Public:    intCalculatestrings) {stack<int>S1; Stack<Char>S2; intCurres =0;  for(inti =0; I <s.size ();) {            if(S[i] = =' ') {i++; }            Else if(S[i] = ='+'|| S[i] = ='-'|| S[i] = ='(') {S2.push (s[i++]); }            Else if(IsDigit (S[i])) {intTMP =0, j =i;  while(J < S.size () &&isdigit (S[j])) {tmp=Ten* tmp + s[j++]-'0';                } s1.push (TMP); I=J; if(!s2.empty () && s2.top ()! ='(') {                    CharCtmp =S2.top ();                    S2.pop (); intsecond, first; Second=S1.top ();                    S1.pop (); First=S1.top ();                    S1.pop (); Curres= Ctmp = ='+'? First + Second:first-second;                S1.push (Curres); }            }            Else{s2.pop ();//(                CharOP ='?'; intFirst =0, second; if(!S2.empty ()) {op=S2.top ();                    S2.pop (); Second=S1.top ();                    S1.pop (); if(!S1.empty ()) { First=S1.top ();                    S1.pop (); }                    if(OP = ='+') {S1.push ( first+second); }                    Else if(OP = ='-') {S1.push ( first-second); }                    Else{S1.push (second); }} I++; }        }        returnS1.empty ()?0: S1.top (); }};

Later on the internet found a more concise wording, reference https://www.cnblogs.com/newnoobbird/p/9627182.html. Very concise, the use of

classSolution { Public:    intCalculatestrings) {intres=0, sign=1, n=s.size (); Stack<int>St;  for(intI=0; i<n;i++){            if(s[i]>='0'){                intnum=0;  while(i<n&&s[i]>='0') {num=num*Ten+s[i++]-'0'; } Res+=sign*num; I--; }Else if(s[i]=='+') { sign=1; }Else if(s[i]=='-') { sign=-1; }Else if(s[i]=='(') {St.push (res);                St.push (sign); Res=0; sign=1; }Else if(s[i]==')') {res*=st.top (); St.pop (); Res+=st.top (); St.pop (); }        }        returnRes; }};

Leetcode 224. Basic Calculator