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Merge pull request onlyliuxin#182 from DonaldY/master
24组 第6周作业
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‎group24/1148285693/learning2017/learning-basic/src/main/java/me/lzb/basic/InfixExpr.java

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‎group24/1148285693/learning2017/learning-basic/src/main/java/me/lzb/basic/expr/CalUtil.java

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package me.lzb.basic.expr;
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import me.lzb.common.utils.StringUtils;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.Stack;
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/**
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* Created by LZB on 2017/4/20.
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*/
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public class CalUtil {
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public static void calculate(Stack<String> symbolStack, Stack<Float> numberStack, boolean isRe) {
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if (symbolStack.isEmpty()) {
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return;
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}
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String symbole = symbolStack.pop();
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float right;
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float left;
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if (isRe) {
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left = numberStack.pop();
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right = numberStack.pop();
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} else {
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right = numberStack.pop();
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left = numberStack.pop();
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}
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float r = calculate(symbole, left, right);
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numberStack.push(r);
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}
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public static float calculate(String symbol, float left, float right) {
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if ("+".equals(symbol)) {
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return left + right;
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}
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if ("-".equals(symbol)) {
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return left - right;
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}
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if ("*".equals(symbol)) {
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return left * right;
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}
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if ("/".equals(symbol)) {
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return left / right;
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}
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return 0;
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}
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public static List<Node> processInfixExpr(String expr) {
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List<Node> list = new ArrayList<>();
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char[] array = expr.toCharArray();
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String number = "";
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for (int i = 0; i < array.length; i++) {
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if (Character.isDigit(array[i])) {
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number = number + String.valueOf(array[i]);
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} else {
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if (StringUtils.isNotBlank(number)) {
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Node num = new Node(Float.valueOf(number), null, -1);
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number = "";
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list.add(num);
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}
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int calLevel = 1;
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if ("*/".indexOf(array[i]) >= 0) {
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calLevel = 2;
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}
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if ("()".indexOf(array[i]) >= 0) {
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calLevel = 3;
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}
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Node sym = new Node(0, String.valueOf(array[i]), calLevel);
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list.add(sym);
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}
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}
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if (StringUtils.isNotBlank(number)) {
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Node num = new Node(Float.valueOf(number), null, -1);
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list.add(num);
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}
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return list;
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}
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public static boolean isLowLevel(Node stackTop, Node next) {
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return stackTop.calLevel < next.calLevel;
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}
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public static void main(String[] args) {
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Node n = new Node(0, "*", 2);
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Node m = new Node(0, "-", 1);
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System.out.println(isLowLevel(n, m));
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}
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}

‎group24/1148285693/learning2017/learning-basic/src/main/java/me/lzb/basic/expr/InfixExpr.java

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package me.lzb.basic.expr;
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import java.util.List;
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import java.util.Stack;
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/**
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* 中序表达式
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* Created by LZB on 2017/4/15.
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*/
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public class InfixExpr {
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private String expr;
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public InfixExpr(String expr) {
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this.expr = expr;
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}
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public float evaluate() {
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List<Node> list = CalUtil.processInfixExpr(expr);
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Stack<String> symbolStack = new Stack<>();
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Stack<Float> numberStack = new Stack<>();
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boolean calLevel2 = false;
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for (Node n : list) {
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if (n.isNumber()) {
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numberStack.push(n.number);
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if (calLevel2) {
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CalUtil.calculate(symbolStack, numberStack, false);
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calLevel2 = false;
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}
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} else {
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symbolStack.push(n.symbol);
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if (n.isLevel2()) {
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calLevel2 = true;
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}
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}
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}
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Stack<Float> tn = new Stack<>();
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int nsize = numberStack.size();
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for (int i = 0; i < nsize; i++) {
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tn.push(numberStack.pop());
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}
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numberStack = tn;
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Stack<String> ts = new Stack<>();
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int ssize = symbolStack.size();
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for (int i = 0; i < ssize; i++) {
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ts.push(symbolStack.pop());
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}
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symbolStack = ts;
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while (!symbolStack.isEmpty()) {
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CalUtil.calculate(symbolStack, numberStack, true);
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}
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return numberStack.pop();
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}
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}

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