标签:rgs 计算 link tle ringbuf array default message stat
RingBuffer面试后面一场,输入一个字符串,计算结果
字符串内容限制为“ 0-9,+,-,*,/”这些符号
例如输入"1+2*3/4-5",返回-2.5。
开始到时候直接想到了可以用树来维护计算关系,后来被问可以用其他数据结构么,然后想到应该用栈来实现,写的时候用了一个,写到后面突然意识到应该用两个栈,一个存数据,一个存操作符。
在家里写了完成大概写了一个小时不到,当时是没写完,后来口述了一下逻辑。
重点在于:
1.第一个符号到判断,可能第一个字符是“+”或者“-”。
2.末尾非法符号判断。
3.中间连续连个操作符的判断。
具体是几行粗体代码
package com.ljw.javatest; import java.util.LinkedList; import java.util.Stack; public class Calculate { public static void print(Object value) { System.out.println(value); } public static void main(String[] args) throws Exception { String input = null; input = "1+2*3/4-5"; print(calculate(input) == -2.5); input = "-1+2*3/4-5"; print(calculate(input) == -4.5); try { input = ""; calculate(input); } catch (Exception ex) { print(ex.getMessage().equals(exMsg)); } try { input = null; calculate(input); } catch (Exception ex) { print(ex.getMessage().equals(exMsg)); } try { input = "1+2*3/4-a5"; calculate(input); } catch (Exception ex) { print(ex.getMessage().equals(exMsg)); } try { input = "1+2*a3/4-5"; calculate(input); } catch (Exception ex) { print(ex.getMessage().equals(exMsg)); } try { input = "1+2**3/4-5"; calculate(input); } catch (Exception ex) { print(ex.getMessage().equals(exMsg)); } try { input = "1+2*3/4+-5"; calculate(input); } catch (Exception ex) { print(ex.getMessage().equals(exMsg)); } try { input = "1+-2*3/4-5"; calculate(input); } catch (Exception ex) { print(ex.getMessage().equals(exMsg)); } try { input = "1-2*3/4-5-"; calculate(input); } catch (Exception ex) { print(ex.getMessage().equals(exMsg)); } } static String exMsg = "invalid input"; public static double calculate(String input) throws Exception { if (input == null || input.length() == 0) { throw new Exception(exMsg); } char[] arr = input.toCharArray(); Stack<Double> valueStack = new Stack(); Stack<String> opStack = new Stack(); StringBuilder sb = new StringBuilder(); boolean flag = false; for (int i = 0; i < arr.length; i++) { char temp = arr[i]; if (temp != ‘+‘ && temp != ‘-‘ && temp != ‘*‘ && temp != ‘/‘) { if (temp < ‘0‘ || temp > ‘9‘) { throw new Exception(exMsg); } sb.append(temp); continue; } Double value = null; if (sb.length() != 0) { value = Double.parseDouble(sb.toString()); sb.setLength(0); } if(i<arr.length-1 &&!(arr[i+1] != ‘+‘ && arr[i+1] != ‘-‘ && arr[i+1] != ‘*‘ && arr[i+1] != ‘/‘)){ throw new Exception(exMsg); } if(i==arr.length-1){ throw new Exception(exMsg); } if (flag) { if (value == null) { throw new Exception(exMsg); } Double a = valueStack.pop(); String op = opStack.pop(); switch (op) { case "*": value = a * value; break; case "/": value = a / value; break; // default: // throw new Exception(exMsg); } valueStack.push(value); } else { if (value != null) { valueStack.push(value); } } opStack.push(String.valueOf(temp)); if (temp == ‘+‘ || temp == ‘-‘) { flag = false; } else { flag = true; } } // if (sb.length() == 0) { // throw new Exception(exMsg); // } valueStack.push(Double.parseDouble(sb.toString())); double result = valueStack.pop(); while (!valueStack.isEmpty() && !opStack.isEmpty()) { double value = valueStack.pop(); String op = opStack.pop(); // 第一个输入可能是带符号 if (valueStack.isEmpty() && opStack.size() == 1) { String extra = opStack.pop(); if (extra.equals("-")) { value = 0 - value; } } switch (op) { case "-": result = value - result; break; case "+": result = value + result; break; // default: // throw new Exception(exMsg); } } // if (!valueStack.isEmpty() || !opStack.isEmpty()) { // throw new Exception(exMsg); // } return result; } }
标签:rgs 计算 link tle ringbuf array default message stat
原文地址:https://www.cnblogs.com/lvjianwei/p/11167382.html