[LeetCode] 150. Evaluate Reverse Polish Notation

发布于 2018-12-13  约 4 分钟

Problem

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are +, -, *, /. Each operand may be an integer or another expression.

Note:

Division between two integers should truncate toward zero.
The given RPN expression is always valid. That means the expression would always evaluate to a result and there won't be any divide by zero operation.
Example 1:

Input: ["2", "1", "+", "3", "*"]
Output: 9
Explanation: ((2 + 1) * 3) = 9
Example 2:

Input: ["4", "13", "5", "/", "+"]
Output: 6
Explanation: (4 + (13 / 5)) = 6
Example 3:

Input: ["10", "6", "9", "3", "+", "-11", "", "/", "", "17", "+", "5", "+"]
Output: 22
Explanation:
((10 (6 / ((9 + 3) -11))) + 17) + 5
= ((10 (6 / (12 -11))) + 17) + 5
= ((10 * (6 / -132)) + 17) + 5
= ((10 * 0) + 17) + 5
= (0 + 17) + 5
= 17 + 5
= 22

Solution

class Solution {
    public int evalRPN(String[] tokens) {
        Deque<Integer> stack = new ArrayDeque<>();
        for (String token: tokens) {
            if (token.equals("+")) {
                stack.push(stack.pop()+stack.pop());
            } else if (token.equals("-")) {
                stack.push(-stack.pop()+stack.pop());
            } else if (token.equals("*")) {
                stack.push(stack.pop()*stack.pop());
            } else if (token.equals("/")) {
                int divisor = stack.pop();
                int dividend = stack.pop();
                stack.push(dividend/divisor);
            } else {
                stack.push(Integer.parseInt(token));
            }
        }
        return stack.pop();
    }
}
阅读 629发布于 2018-12-13

推荐阅读
Road to Glory
用户专栏

對酒當歌,人生幾何?譬如朝露,去日苦多。

22 人关注
639 篇文章
专栏主页
目录