/** * */package com.plxue.interview.algorithm.stack;import java.util.Arrays;import java.util.List;import java.util.Stack;import org.slf4j.Logger;import org.slf4j.LoggerFactory;/* // @author matrix // Jan 23, 2013 // 表达式求值(Expression Evaluation) // 基本规则 // 1. 先乘除，后加减 // 2. 从左算到右 // 3. 先括号内，后括号外 */public class ExpressionEvaluation {private static Logger LOG = LoggerFactory.getLogger(ExpressionEvaluation.class);private static List<Character> ops = Arrays.asList('+', '-', '*', '/', '(',')', '[', ']', '{', '}', '#');// ------------------ 左操作符跟右操作符优先级关系表 -------------------// |------'+', '-', '*', '/', '(', ')', '[', ']', '{', '}', '#'--|// |-------------------------------------------------------------|private static char[][] prioTable = new char[][] {{ '>', '>', '<', '<', '<', '>', '<', '>', '<', '>', '>' }, // +{ '>', '>', '<', '<', '<', '>', '<', '>', '<', '>', '>' }, // -{ '>', '>', '>', '>', '<', '>', '<', '>', '<', '>', '>' }, // *{ '>', '>', '>', '>', '<', '>', '<', '>', '<', '>', '>' }, // /{ '<', '<', '<', '<', '<', '=', ' ', ' ', ' ', ' ', ' ' }, // ({ '>', '>', '>', '>', ' ', '>', ' ', ' ', ' ', ' ', '>' }, // ){ '<', '<', '<', '<', '<', ' ', '<', '=', ' ', ' ', ' ' }, // [{ '>', '>', '>', '>', ' ', ' ', '=', ' ', ' ', '>', '>' }, // ]{ '<', '<', '<', '<', '<', ' ', '<', ' ', '<', '=', ' ' }, // {{ '>', '>', '>', '>', ' ', ' ', ' ', ' ', '=', '>', '>' }, // }{ '<', '<', '<', '<', '<', ' ', '<', ' ', '<', ' ', '=' } }; // #public static char precede(char l, char r) {return prioTable[ops.indexOf(l)][ops.indexOf(r)];}public static double operate(double l, double r, char op) {switch (op) {case '+':return l + r;case '-':return l - r;case '*':return l * r;case '/':return l / r;}return 0;}public static double evaluation(String expression) {// process expressionexpression = expression.replaceAll("\\s+", "");expression += '#';Stack<Double> operands = new Stack<Double>();Stack<Character> operators = new Stack<Character>();operators.push('#');int index = 0;while (expression.charAt(index) != '#' || operators.peek() != '#') {if (!ops.contains(expression.charAt(index))) {int end = index;for (; end < expression.length(); ++end) {if (ops.contains(expression.charAt(end + 1)))break;}operands.push(Double.parseDouble(expression.substring(index,end + 1)));index = end + 1;} else {switch (precede(operators.peek(), expression.charAt(index))) {case '<':operators.push(expression.charAt(index++));break;case '=':operators.pop();index++;break;case '>':char op = operators.pop();double r = operands.pop();double l = operands.pop();operands.push(operate(l, r, op));break;default:throw new IllegalArgumentException(String.format("操作符异常:%c, %c", operators.peek(),expression.charAt(index)));}}}return operands.pop();}/** * @param args */public static void main(String[] args) {String[] expressions = new String[] { "3*(7-2)", "12*(14-2)+5","1.1 + 2.5 * 2.2 * (2 - 5)", "{[2+3*2/(1+1)]*3+5}","3*5+2-4*[1+3*(2-5)]", "[)3*3]", "{(3+2)*5 + 3*2}" };for (String exp : expressions) {try {LOG.debug(String.format("exp:%s, result:%.2f", exp,evaluation(exp)));} catch (Exception e) {LOG.error(e.getMessage(), e);}}}}
