题解 | #牛的表达式计算器#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param tokens string字符串一维数组
     * @return int整型
     */
    public int calculatePostfix (String[] tokens) {
        // write code here
        Stack<Integer> stack = new Stack<>();
        int sum = 0;
        for (String token : tokens) {
            boolean flag = Character.isDigit(token.charAt(token.length() - 1));
            if (!flag) {
                if (token.equals("+")) {
                    sum = stack.pop() + stack.pop();
                    stack.push(sum);
                }
                if (token.equals("-")) {
                    int last = stack.pop();
                    sum = stack.pop() - last;
                    stack.push(sum);
                }
                if (token.equals("*")) {
                    sum = stack.pop() * stack.pop();
                    stack.push(sum);
                }
                if (token.equals("/")) {
                    int last = stack.pop();
                    sum = stack.pop() / last;
                    stack.push(sum);
                }
            } else {
                stack.push(Integer.parseInt(token));
            }
        }
        return stack.pop();
    }
}