第一次寫博客。。。編譯原理課的一個實驗。

　　感覺自己花了挺長的時間，所以作為博客保留下來，挺有紀念意義的??（因為我是菜鳥）

package com.insist.entity;import java.util.ArrayList; import java.util.List; import java.util.Scanner;/*** * @author SNOOPY 消除一切左遞歸*/ public class EliminateLeftRecursion {private static int n;// 實際輸入產生式個數public static void main(String[] args) {Scanner scan = new Scanner(System.in);System.out.println("請輸入產生式個數：");n = scan.nextInt();// 創建產生式數組存放輸入的產生式List<Regular> regulars = new ArrayList<Regular>();for (int i = 0; i < n; i++) {Regular reg = new Regular();System.out.println("請輸入產生式左部:");String left = scan.next();reg.setLeft(left);System.out.println("請輸入產生式的右部:");String right = scan.next();reg.setRight(right);regulars.add(reg);}/** 測試輸出------->成功 for (Regular reg: regulars) { System.out.println(reg.getLeft()+"---->"+reg.getRight()); }*/// 構造一個字符型的數組用來存放排序好的非終結符String[] Vn = new String[50];// 對所有的產生式按照一定的順序存放Vn[0] = regulars.get(0).getLeft();// 把產生式第一個非終結符放到集合中int flag = 0;int count = 0;for (int i = 1; i < n; i++) {// 對非終結符排序并存取 1、遍歷產生式數組for (int j = 0; j < i; j++) {// 如果產生式左部等于在它前面的產生式的左部if (regulars.get(i).getLeft().equals(regulars.get(j).getLeft())) {// 說明有重復的flag++;}}if (flag == 0) {// 說明沒有重復，則加入非終結符數組中count++;Vn[count] = regulars.get(i).getLeft();}flag = 0;}/** 測試非終結符數組------------>成功 for (int i = 0; i < Vn.length; i++) { if(Vn[i]!=null){ System.out.println(Vn[i]); } }*/for (Regular reg : regulars) {if (reg != null) {System.out.println(reg.getLeft() + "---->" + reg.getRight());}}regulars = subFunction(regulars, Vn, count);for (Regular reg : regulars) {if (reg != null) {System.out.println(reg.getLeft() + "---->" + reg.getRight());}}}public static List<Regular> subFunction(List<Regular> regulars, String[] Vn, int count) {int flag = 0;// 判斷是否存在間接左遞歸并轉化為直接左遞歸for (int i = 0; i <= count; i++) {// 對每一個非終結符 迭代for (int j = 0; j < i; j++) {// 對每一個小于i的非終結符遍歷for (int k = 0; k < regulars.size(); k++) // 對每一個產生式if (Vn[i].equals(regulars.get(k).getLeft())) {// i非終結符與第k產生式左邊第一個字母相等-->鎖定非終結符集合中的一個非終結符的產生式if (regulars.get(k).getRight().substring(0, 1).equals(Vn[j])) { // g產生式右邊產生式第一個符號與第j個非終結符相等-->說明存在間接左遞歸for (int h = 0; h < regulars.size(); h++) {if (regulars.get(h).getLeft().equals(Vn[j])) {// 進行替換 String str;str = regulars.get(k).getRight().substring(1);// 截取右邊第一個以后的字符Regular reg = new Regular();reg.setLeft(regulars.get(k).getLeft());reg.setRight(regulars.get(h).getRight() + str);regulars.add(reg);}}regulars.remove(k);}}}}// 消除所有直接左遞歸for (int i = 0; i <= count; i++) {flag = 0;for (int j = 0; j < regulars.size(); j++) {// 判斷是否存在直接左遞歸if (regulars.get(j).getLeft().equals(Vn[i])) {System.out.println(regulars.get(j).getLeft() + " ======= " + Vn[i]);if (regulars.get(j).getLeft().equals(regulars.get(j).getRight().substring(0, 1))) {System.out.println("消除間接左遞歸后存在直接左遞歸");flag++;}}}if (flag != 0) {// 存在直接左遞歸for (int j = 0; j < regulars.size(); j++) {if (regulars.get(j).getLeft().equals(Vn[i])) {// 尋找與存在直接左遞歸的非終結符左部相同的的產生式if (regulars.get(j).getLeft().equals(regulars.get(j).getRight().substring(0, 1))) {// 直接左遞歸的產生式String str = regulars.get(j).getRight().substring(1);String temp = regulars.get(j).getLeft();String temp1 = "'";regulars.get(j).setLeft(temp + temp1);regulars.get(j).setRight(str + regulars.get(j).getLeft());Regular reg = new Regular();reg.setLeft(regulars.get(j).getLeft());reg.setRight("ε");regulars.add(reg);} else {String temp = regulars.get(j).getLeft();String temp1 = "'";temp = temp + temp1;regulars.get(j).setRight(regulars.get(j).getRight() + temp);}}}}}return regulars;} } package com.insist.entity;import java.io.Serializable;/*** * @author SNOOPY**/ public class Regular implements Serializable {private static final long serialVersionUID = 1L;private String right;// 定義產生式右部private String left;// 定義產生式左部public String getRight() {return right;}public void setRight(String right) {this.right = right;}public String getLeft() {return left;}public void setLeft(String left) {this.left = left;} }

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轉載于:https://www.cnblogs.com/snoopylovefiona/p/4593726.html

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