剑指 Offer II 036. 后缀表达式

class Solution:
    def evalRPN(self, tokens: List[str]) -> int:
        nums = []
        for t in tokens:
            if len(t) > 1 or t.isdigit():
                nums.append(int(t))
            else:
                if t == "+":
                    nums[-2] += nums[-1]
                elif t == "-":
                    nums[-2] -= nums[-1]
                elif t == "*":
                    nums[-2] *= nums[-1]
                else:
                    nums[-2] = int(nums[-2] / nums[-1])
                nums.pop()
        return nums[0]

class Solution {
    public int evalRPN(String[] tokens) {
        Deque<Integer> stk = new ArrayDeque<>();
        for (String t : tokens) {
            if (t.length() > 1 || Character.isDigit(t.charAt(0))) {
                stk.push(Integer.parseInt(t));
            } else {
                int y = stk.pop();
                int x = stk.pop();
                switch (t) {
                case "+":
                    stk.push(x + y);
                    break;
                case "-":
                    stk.push(x - y);
                    break;
                case "*":
                    stk.push(x * y);
                    break;
                default:
                    stk.push(x / y);
                    break;
                }
            }
        }
        return stk.pop();
    }
}

class Solution {
public:
    int evalRPN(vector<string>& tokens) {
        stack<int> stk;
        for (auto& t : tokens) {
            if (t.size() > 1 || isdigit(t[0])) {
                stk.push(stoi(t));
            } else {
                int y = stk.top();
                stk.pop();
                int x = stk.top();
                stk.pop();
                if (t[0] == '+')
                    stk.push(x + y);
                else if (t[0] == '-')
                    stk.push(x - y);
                else if (t[0] == '*')
                    stk.push(x * y);
                else
                    stk.push(x / y);
            }
        }
        return stk.top();
    }
};

func evalRPN(tokens []string) int {
	// https://github.com/emirpasic/gods#arraystack
	stk := arraystack.New()
	for _, token := range tokens {
		if len(token) > 1 || token[0] >= '0' && token[0] <= '9' {
			num, _ := strconv.Atoi(token)
			stk.Push(num)
		} else {
			y := popInt(stk)
			x := popInt(stk)
			switch token {
			case "+":
				stk.Push(x + y)
			case "-":
				stk.Push(x - y)
			case "*":
				stk.Push(x * y)
			default:
				stk.Push(x / y)
			}
		}
	}
	return popInt(stk)
}

func popInt(stack *arraystack.Stack) int {
	v, _ := stack.Pop()
	return v.(int)
}