150. Evaluate Reverse Polish Notation

Question

Solution

2 1 + 3 * 是((2+1)*3)的后缀(postfix)或逆波兰(reverse Polish)记法，计算这个表达式容易想到栈，当见到一个数时就入栈，见到操作符时该运算符作用于从该栈中弹出的两个数上，将所得结果入栈。

public int evalRPN(String[] tokens) {

    Stack<Integer> stack = new Stack<>();

    for (String tmp : tokens) {

        if (tmp.length() > 1) {

            stack.push(Integer.parseInt(tmp));

            continue;

        }

        char c = tmp.charAt(0); // String转char

        int a, b;

        switch (c) {

            case '+':

                b = stack.pop();

                a = stack.pop();

                stack.push(a + b);

                break;

            case '-':

                b = stack.pop();

                a = stack.pop();

                stack.push(a - b);

                break;

            case '*':

                b = stack.pop();

                a = stack.pop();

                stack.push(a * b);

                break;

            case '/':

                b = stack.pop();

                a = stack.pop();

                stack.push(a / b);

                break;

            default:

                stack.push(c - '0'); // char 转 int

        }

    }

    return stack.pop();

}

Reference

https://gitee.com/okokabcd/leetcode

巴特西

150. Evaluate Reverse Polish Notation - LeetCode

Question

Solution

Reference

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