《java数据结构与算法》笔记-CH4-8栈结构实现后缀表达式计算结果

/** * 中缀表达式转换成后缀表达式： 从输入（中缀表达式）中读取的字符，规则： 操作数： 写至输出 左括号： 推其入栈 右括号： 栈非空时重复以下步骤--> * 若项不为(,则写至输出； 若项为(，则推出循环 operator(opThis): 若栈为空，推opThis； 否则，重复--> * 弹出一项，若项为(,推其入栈； 若项为operator，且 若opTop<opThis,推入opTop,或 若opTop>=opThis,输出opTop, * 若opTop<opThis则退出循环，或项为( 推入opThis 没有更多项： 当栈非空时，弹出项目，将其输出 *  */class StackI {private int maxSize;private char[] stack;private int top;public StackI(int size) {maxSize = size;stack = new char[size];top = -1;}public void push(char value) {stack[++top] = value;}public char pop() {return stack[top--];}public char peek() {return stack[top];}public char peekN(int index) {return stack[index];}public int size() {return top + 1;}public boolean isFull() {return top == maxSize;}public boolean isEmpty() {return top == -1;}@Overridepublic String toString() {StringBuilder sb = new StringBuilder();sb.append("[");for (int i = 0; i < size(); i++) {sb.append(peekN(i) + ",");}sb.deleteCharAt(sb.length() - 1);sb.append("]");return sb.toString();}public void display() {System.out.print("当前栈: " + toString());}}class InToPost {private String input, output;private StackI stack;public InToPost(String in) {input = in;output = "";int stackSize = input.length();stack = new StackI(stackSize);}public void gotOper(char opThis, int prec1) {while (!stack.isEmpty()) {char opTop = stack.pop();if (opTop == '(') {stack.push(opTop);break;} else {int prec2;if (opTop == '+' || opTop == '-')prec2 = 1;elseprec2 = 2;if(prec2<prec1){stack.push(opTop);break;}else{output += opTop;}}}stack.push(opThis);}public void gotParen(char ch){while(!stack.isEmpty()){char chx = stack.pop();if(chx == '(')break;elseoutput += chx;}}public String doTrans() {for (int i = 0; i < input.length(); i++) {char ch = input.charAt(i);switch (ch) {case '+':case '-':gotOper(ch, 1);break;case '*':case '/':gotOper(ch, 2);break;case '(':stack.push(ch);break;case ')':gotParen(ch);break;default:output += ch;break;}}while(!stack.isEmpty()){output += stack.pop();}return output;}/** * 计算后缀表达式结果 * 遇到操作数--入栈 * 遇到操作符--从栈中提取两个操作数，用操作符执行运算，结果入栈 * 注：这里转换后缀和计算后缀表达式共用了一个栈类型Model，所以在计算过程中字符和int转换时多了一些操作 * @param in * @return */public int doParse(String in){stack = new StackI(20);int num1,num2,result = 0;int j;char c;for(j=0;j<in.length();j++){c = in.charAt(j);if(c>='0' && c<='9'){stack.push(c);}else{num2 = (int)(stack.pop()-'0');num1 = (int)(stack.pop()-'0');switch (c) {case '+':result = num1+num2;break;case '-':result = num1-num2;break;case '*':result = num1*num2;break;case '/':result = num1/num2;break;default:result = 0;break;}stack.push((char)(result+'0'));}}result = (int)(stack.pop()-'0');return result;}}public class InfixDemo {/** * 读取字符串 *  * @return * @throws IOException */public static String getString() throws IOException {InputStreamReader isr = new InputStreamReader(System.in);BufferedReader reader = new BufferedReader(isr);return reader.readLine();}public static void main(String[] args) throws IOException {String input, output;while(true){System.out.println("enter:");System.out.flush();input = getString();if(input.equals(""))break;InToPost i = new InToPost(input);output = i.doTrans();System.out.println(output);System.out.println(i.doParse(output));}}}