算法1

Java 代码

class Solution {
    private final static Map<String, BiFunction<Integer, Integer, Integer>> map = new HashMap<>();
    static{
        map.put("+", (a,b)->a+b);
        map.put("-", (a,b)->a-b);
        map.put("*", (a,b)->a*b);
        map.put("/", (a,b)->a/b);
    }

    public int evalRPN(String[] tokens) {
        Stack<Integer> stack = new Stack<>();
        for(String s:tokens){
            if(map.containsKey(s)){
                int num2 = stack.pop();
                int num1 = stack.pop();
                BiFunction<Integer, Integer, Integer> operation = map.get(s);
                int res = operation.apply(num1, num2);
                stack.push(res);
            }else{
                stack.push(Integer.valueOf(s));
            }
        }
        return stack.pop();
    }
}