[LeetCode] 224. Basic Calculator 基本计算器

Implement a basic calculator to evaluate a simple expression string.

The expression string may contain open ( and closing parentheses ), the plus + or minus sign -, non-negative integers and empty spaces .

You may assume that the given expression is always valid.

Some examples:

"1 + 1" = 2
" 2-1 + 2 " = 3
"(1+(4+5+2)-3)+(6+8)" = 23

Note: Do not use the eval built-in library function.

 

Java:

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public int calculate(String s) {     // delte white spaces     s = s.replaceAll(" ", "");        Stack<String> stack = new Stack<String>();     char[] arr = s.toCharArray();        StringBuilder sb = new StringBuilder();     for (int i = 0; i < arr.length; i++) {         if (arr[i] == ' ')             continue;            if (arr[i] >= '0' && arr[i] <= '9') {             sb.append(arr[i]);                if (i == arr.length - 1) {                 stack.push(sb.toString());             }         } else {             if (sb.length() > 0) {                 stack.push(sb.toString());                 sb = new StringBuilder();             }                if (arr[i] != ')') {                 stack.push(new String(new char[] { arr[i] }));             } else {                 // when meet ')', pop and calculate                 ArrayList<String> t = new ArrayList<String>();                 while (!stack.isEmpty()) {                     String top = stack.pop();                     if (top.equals("(")) {                         break;                     } else {                         t.add(0, top);                     }                 }                    int temp = 0;                 if (t.size() == 1) {                     temp = Integer.valueOf(t.get(0));                 } else {                     for (int j = t.size() - 1; j > 0; j = j - 2) {                         if (t.get(j - 1).equals("-")) {                             temp += 0 - Integer.valueOf(t.get(j));                         } else {                             temp += Integer.valueOf(t.get(j));                         }                     }                     temp += Integer.valueOf(t.get(0));                 }                 stack.push(String.valueOf(temp));             }         }     }        ArrayList<String> t = new ArrayList<String>();     while (!stack.isEmpty()) {         String elem = stack.pop();         t.add(0, elem);     }        int temp = 0;     for (int i = t.size() - 1; i > 0; i = i - 2) {         if (t.get(i - 1).equals("-")) {             temp += 0 - Integer.valueOf(t.get(i));         } else {             temp += Integer.valueOf(t.get(i));         }     }     temp += Integer.valueOf(t.get(0));        return temp; }

Python:

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class Solution:     # @param {string} s     # @return {integer}     def calculate(self, s):         operands, operators = [], []         operand = ""         for i in reversed(xrange(len(s))):             if s[i].isdigit():                 operand += s[i]                 if i == 0  or not s[i-1].isdigit():                     operands.append(int(operand[::-1]))                     operand = ""             elif s[i] == ')' or s[i] == '+' or s[i] == '-':                 operators.append(s[i])             elif s[i] == '(':                 while operators[-1] != ')':                     self.compute(operands, operators)                 operators.pop()                           while operators:             self.compute(operands, operators)                       return operands[-1]       def compute(self, operands, operators):         left, right = operands.pop(), operands.pop()         op = operators.pop()         if op == '+':             operands.append(left + right)         elif op == '-':             operands.append(left - right)

C++:

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class Solution { public:     int calculate(string s) {         int res = 0, sign = 1, n = s.size();         stack<int> st;         for (int i = 0; i < n; ++i) {             char c = s[i];             if (c >= '0') {                 int num = 0;                 while (i < n && s[i] >= '0') {                     num = 10 * num + s[i++] - '0';                 }                 res += sign * num;                 --i;             } else if (c == '+') {                 sign = 1;             } else if (c == '-') {                 sign = -1;             } else if (c == '(') {                 st.push(res);                 st.push(sign);                 res = 0;                 sign = 1;             } else if (c == ')') {                 res *= st.top(); st.pop();                 res += st.top(); st.pop();             }         }         return res;     } };

C++:

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class Solution2 { public:     int calculate(string s) {         stack<int> operands;         stack<char> operators;         string operand;         for (int i = s.length() - 1; i >= 0; --i) {             if (isdigit(s[i])) {                 operand.push_back(s[i]);                 if (i == 0 || !isdigit(s[i - 1])) {                     reverse(operand.begin(), operand.end());                     operands.emplace(stoi(operand));                     operand.clear();                 }             } else if (s[i] == ')' || s[i] == '+' || s[i] == '-') {                 operators.emplace(s[i]);             } else if (s[i] == '(') {                 while (operators.top() != ')') {                     compute(operands, operators);                 }                 operators.pop();             }         }         while (!operators.empty()) {             compute(operands, operators);         }         return operands.top();     }       void compute(stack<int>& operands, stack<char>& operators) {         const int left = operands.top();         operands.pop();         const int right = operands.top();         operands.pop();         const char op = operators.top();         operators.pop();         if (op == '+') {             operands.emplace(left + right);         } else if (op == '-') {             operands.emplace(left - right);         }     } };

　　　　

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[LeetCode] 227. Basic Calculator II 基本计算器 II

 

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