BasicCalculatorII.cpp

/* solution 1 */
class Solution {
public:
    int calculateNum(string &s, int &c) {
        int result = 0;
        while (c < s.length() && s[c] != '+' && s[c] != '-' && s[c] != '*' && s[c] != '/') {
            if (s[c] >= '0' && s[c] <= '9') {
                result = result * 10 + s[c] - '0';
            }
            c++;
        }
        return result;
    }
    int calculateMult(string &s, int &c) {
        int result = 1;
        bool div = false;
        while (c < s.length()) {
            if (div) {
                result = result / calculateNum(s, c);
            } else {
                result = result * calculateNum(s, c);
            }
            div = s[c] == '/';
            if (s[c] == '+' || s[c] == '-')
                break;
            c++;
        }
        return result;
    }
    int calculateSums(string &s, int &c) {
        int result = 0;
        int sign = 1;
        while (c < s.length()) {
            result += sign * calculateMult(s, c);
            sign = s[c++] == '+' ? 1 : -1;
        }
        return result;
    }
    int calculate(string s) {
        int current = 0;
        return calculateSums(s, current);
    }
};

/* solution 2 */
class Expr {
    public:
   virtual int eval() = 0; 
};

class BinaryExpr: public Expr {
    public:
    BinaryExpr(Expr *l, Expr *r, char o) {
        left = l;
        right = r;
        op = o;
    }
    int eval() {
        if (op == '+')
            return left->eval() + right->eval();
        else if (op == '-')
            return left->eval() - right->eval();
        else if (op == '*')
            return left->eval() * right->eval();
        else
            return left->eval() / right->eval();
    }
    Expr *left;
    Expr *right;
    char op;
};

class IntValueExpr: public Expr {
    public:
    IntValueExpr(int v) {
        value = v;
    }
    int eval() {
        return value;
    }
    int value;
};

class Solution {
public:
    Expr* parseNum(string &s, int &c) {
        int value = 0;
        while (c < s.length() && s[c] != '+' && s[c] != '-' && s[c] != '*' && s[c] != '/') {
            if (s[c] >= '0' && s[c] <= '9') {
                value = value * 10 + s[c] - '0';
            }
            c++;
        }
        return new IntValueExpr(value);
    }
    Expr* parseLeftAssocMult(string &s, int &c) {
        Expr* result = parseNum(s, c);
        while (s[c] == '*' || s[c] == '/') {
            char op = s[c];
            c++;
            result = new BinaryExpr(result, parseNum(s, c), op);
        }
        return result;
    }
    Expr* parseLeftAssocSum(string &s, int &c) {
        Expr* result = parseLeftAssocMult(s, c);
        while (s[c] == '+' || s[c] == '-') {
            char op = s[c];
            c++;
            result = new BinaryExpr(result, parseLeftAssocMult(s, c), op);
        }
        return result;
    }
    int calculate(string s) {
        int current = 0;
        return parseLeftAssocSum(s, current)->eval();
    }
};

/* solution 3 */
class Expr {
    public:
   virtual int eval() = 0; 
};

class BinaryExpr: public Expr {
    public:
    BinaryExpr(Expr *l, Expr *r, char o) {
        left = l;
        right = r;
        op = o;
    }
    int eval() {
        if (op == '+')
            return left->eval() + right->eval();
        else if (op == '-')
            return left->eval() - right->eval();
        else if (op == '*')
            return left->eval() * right->eval();
        else
            return left->eval() / right->eval();
    }
    Expr *left;
    Expr *right;
    char op;
};

class IntValueExpr: public Expr {
    public:
    IntValueExpr(int v) {
        value = v;
    }
    int eval() {
        return value;
    }
    int value;
};

class Solution {
public:
    Expr* parseNum(string &s, int &c) {
        int value = 0;
        while (isdigit(s[c])) {
            value = value * 10 + s[c] - '0';
            c++;
        }
        return new IntValueExpr(value);
    }
    Expr* parseLeftAssocMult(string &s, int &c) {
        Expr* result = parseNum(s, c);
        while (s[c] == '*' || s[c] == '/') {
            char op = s[c];
            c++;
            result = new BinaryExpr(result, parseNum(s, c), op);
        }
        return result;
    }
    Expr* parseLeftAssocSum(string &s, int &c) {
        Expr* result = parseLeftAssocMult(s, c);
        while (s[c] == '+' || s[c] == '-') {
            char op = s[c];
            c++;
            result = new BinaryExpr(result, parseLeftAssocMult(s, c), op);
        }
        return result;
    }
    string removeWhitespace(string s) {
        string result;
        for (int i = 0; i < s.length(); i++) {
            if (!isspace(s[i]))
                result += s[i];
        }
        return result;
    }
    int calculate(string s) {
        int current = 0;
        s = removeWhitespace(s);
        return parseLeftAssocSum(s, current)->eval();
    }
};

BasicCalcultor.cpp

class Expr {
    public:
   virtual int eval() = 0; 
};

class BinaryExpr: public Expr {
    public:
    BinaryExpr(Expr *l, Expr *r, char o) {
        left = l;
        right = r;
        op = o;
    }
    int eval() {
        if (op == '+')
            return left->eval() + right->eval();
        else if (op == '-')
            return left->eval() - right->eval();
        else if (op == '*')
            return left->eval() * right->eval();
        else
            return left->eval() / right->eval();
    }
    Expr *left;
    Expr *right;
    char op;
};

class IntValueExpr: public Expr {
    public:
    IntValueExpr(int v) {
        value = v;
    }
    int eval() {
        return value;
    }
    int value;
};

class Solution {
public:
    Expr* parseNum(string &s, int &c) {
        if (s[c] == '(') {
            c++;
            Expr* result = parseLeftAssocSum(s, c);
            c++;
            return result;
        }
        int value = 0;
        while (isdigit(s[c])) {
            value = value * 10 + s[c] - '0';
            c++;
        }
        return new IntValueExpr(value);
    }
    Expr* parseLeftAssocMult(string &s, int &c) {
        Expr* result = parseNum(s, c);
        while (s[c] == '*' || s[c] == '/') {
            char op = s[c];
            c++;
            result = new BinaryExpr(result, parseNum(s, c), op);
        }
        return result;
    }
    Expr* parseLeftAssocSum(string &s, int &c) {
        Expr* result = parseLeftAssocMult(s, c);
        while (s[c] == '+' || s[c] == '-') {
            char op = s[c];
            c++;
            result = new BinaryExpr(result, parseLeftAssocMult(s, c), op);
        }
        return result;
    }
    string removeWhitespace(string s) {
        string result;
        for (int i = 0; i < s.length(); i++) {
            if (!isspace(s[i]))
                result += s[i];
        }
        return result;
    }
    int calculate(string s) {
        int current = 0;
        s = removeWhitespace(s);
        return parseLeftAssocSum(s, current)->eval();
    }
};