题目：

给出如下串：sum(sum(sum(1,2),avg(3,5)),avg(avg(6,8),7))， 计算结果（保证输入任意上述接口均能输出正确结果）

思路：

​编辑
代码：

import java.util.Stack;public class Test {public static String sum = "sum";public static String avg = "avg";public static String s1 = "sum(sum(sum(1,2),avg(3,5)),avg(avg(6,8),7))";public static void main(String[] args) {System.out.println(parseByStack(s1));;}/*** * @param s* @return*/public static float parseByStack(CharSequence s) {Stack<String> operators = new Stack<>();Stack<Float> numbers = new Stack<>();int index = 0;while (index < s.length()) {if (s.charAt(index) == 's' && s.charAt(index + 1) == 'u' && s.charAt(index + 2) == 'm') {operators.push(sum);index += 3;} else if (s.charAt(index) == 'a' && s.charAt(index + 1) == 'v' && s.charAt(index + 2) == 'g') {operators.push(avg);index += 3;} else if (Character.isDigit(s.charAt(index))) {StringBuilder sb = new StringBuilder();while (Character.isDigit(s.charAt(index))) {sb.append(s.charAt(index));index++;}numbers.push(Float.parseFloat(sb.toString()));} else if (s.charAt(index) == ')') {// 遇见左括号时，需要处理数据var operator = operators.pop();if (operator.equals(sum)) {numbers.push(numbers.pop() + numbers.pop());} else if (operator.equals(avg)) {numbers.push((numbers.pop() + numbers.pop()) / 2);}index++;} else {// s.charAt(index) == '(' || s.charAt(index) == ','index++;}}return numbers.pop();}
}