【算法】程序猿不写代码是不对的14

来源：互联网发布：amazon listing 优化编辑：程序博客网时间：2024/04/29 10:04
package com.kingdz.algorithm.time201702;import java.util.HashMap;import java.util.HashSet;import java.util.List;import java.util.Map;import java.util.Set;/** * 算数表达式求值<br/> * 求解思路：按照计算表达式的思考模式，从左到右一次计算，判断每个运算符前后两个临近运算符的优先级来判断计算的方式<br/> * 缺陷：目前在处理中括号和大括号时会有困难 *  * @author kingdz *  */public class Algo08 {// 优先级mappublic static final Map<String, Integer> priorMap;static {priorMap = new HashMap<String, Integer>();priorMap.put("+", 0);priorMap.put("-", 0);//priorMap.put("*", 1);priorMap.put("/", 1);//priorMap.put("(", 2);priorMap.put(")", 2);//priorMap.put("[", 3);priorMap.put("]", 3);//priorMap.put("{", 4);priorMap.put("}", 4);}public static void main(String[] args) {String question = "1+2*(3+4)*5-6";// 将字符串转化为listList<String> list = Algo07.dismantle(question);System.out.print(" ");// 首先打印需要计算的结果printList(list, false);int result = cal(list);// 输出最终计算的结果System.out.println(result);}/** * 打印list，类似于算术 *  * @param list * @param isPrintEquals *            是否在前面打印“=”符号 */private static void printList(List<String> list, boolean isPrintEquals) {StringBuilder strb = new StringBuilder();for (String str : list) {strb.append(str);}if (isPrintEquals) {System.out.println("=" + strb);} else {System.out.println(strb);}}/** * 打印list，类似于算术 *  * @param list */private static void printList(List<String> list) {printList(list, true);}/** * 计算list表达式 *  * @param list * @return */private static int cal(List<String> list) {// 将所有运算符存入set，方便判断是否是运算符Set<String> set = new HashSet<String>();for (String str : Algo07.separator) {set.add(str);}// 用于标记当前处理的位置int index = 0;// 当list的大小为1时表示计算完成while (list.size() > 1) {if (index >= list.size()) {// 如果已经处理到结尾，但是依然没有计算出结果则重新计算index = 0;}// 获得当前处理的字符串String now = list.get(index);{String before2 = index - 2 >= 0 ? list.get(index - 2) : null;String before1 = index - 1 >= 0 ? list.get(index - 1) : null;String after1 = index + 1 < list.size() ? list.get(index + 1) : null;String after2 = index + 2 < list.size() ? list.get(index + 2) : null;if (before1 != null && after1 != null) {{// 用于去括号boolean accord = false;if (before1.equals("(") && after1.equals(")")) {accord = true;} else if (before1.equals("[") && after1.equals("]")) {accord = true;} else if (before1.equals("{") && after1.equals("}")) {accord = true;}if (accord) {list.remove(index + 1);list.remove(index - 1);// index--;index = 0;// System.out.println(list);printList(list);continue;}}// 是运算符if (set.contains(now)) {// 计算前后的优先级int beforePrior2 = getPriority(before2);// int beforePrior1 = getPriority(before1);int nowPrior = getPriority(now);// int afterPrior1 = getPriority(after1);int afterPrior2 = getPriority(after2);if (nowPrior == 1 || (nowPrior == 0 && beforePrior2 != 1 && afterPrior2 != 1)) {int beforeInt;int afterInt;try {beforeInt = Integer.parseInt(list.get(index - 1));afterInt = Integer.parseInt(list.get(index + 1));} catch (NumberFormatException e) {index++;continue;}// 实际进行计算处理boolean accord = false;if ("+".equals(now)) {list.set(index, "" + (beforeInt + afterInt));accord = true;} else if ("-".equals(now)) {list.set(index, "" + (beforeInt - afterInt));accord = true;} else if ("*".equals(now)) {list.set(index, "" + (beforeInt * afterInt));accord = true;} else if ("/".equals(now)) {list.set(index, "" + (beforeInt / afterInt));accord = true;}if (accord) {list.remove(index + 1);list.remove(index - 1);// index--;index = 0;// System.out.println(list);printList(list);continue;}}}}}index++;}return Integer.parseInt(list.get(0));}/** * 根据运算符判断优先级数字 *  * @param str * @return 如果是空则返回-1，如果没有则返回-2 *  */private static int getPriority(String str) {if (str == null) {return -1;}if (priorMap.containsKey(str)) {return priorMap.get(str);} else {return -2;}}}
0 0