package exercise.stack;
/**
-
中缀表达式
-
遇左括号直接放进运算符栈,…遇见右括号,若当前运算符栈顶不是左括号,则退出一个运算符,两个操作数,直到运算符栈顶是和右括号配对的左括号,这时左括号就可以出栈了
-
@ClassName: NifixExpression
-
@author: fan
-
@date: 2020年6月12日 上午11:18:53
-
@version 1.0v
/
public class NifixExpression {
public static void main(String[] args) {
String expression = “13+256-2”;//130
//String expression = "(20+(3(3+1*4+5)-8))*2";// 96
ArrayStack numStack = new ArrayStack(10);
ArrayStack operStack = new ArrayStack(10);// 需要定义的相关变量 int index = 0;// 指针,用来指定当前扫描到第几个数 int num1 = 0; int num2 = 0; int oper = 0; int res = 0; char ch = ' ';// 把每次扫描到的结果保存到ch中 String keepNum = "";// 用于拼接多位数 while (true) { // 2+(3*(1+4*5)-2) // 依次得到每一个数 ch = expressin.substring(index, index + 1).charAt(0); // 判断ch是什么 if (operStack.isOper(ch)) { if (operStack.isLeftBracket(ch) == 0) { operStack.push(ch); } else if (operStack.isLeftBracket(ch) == 1) { while (true) { num1 = numStack.pop(); num2 = numStack.pop(); oper = operStack.pop(); res = operStack.cal(num1, num2, oper); numStack.push(res); if (operStack.peek() == '(') { break; } } // 弹出左括号 operStack.pop(); } else { // 判断是不是空的 if (!operStack.isEmpty()) { if (operStack.peek() == '(') { operStack.push(ch); } else { // 当前这个小于或等于 if (operStack.priority(ch) <= operStack.priority(operStack.peek())) { num1 = numStack.pop(); num2 = numStack.pop(); oper = operStack.pop(); res = operStack.cal(num1, num2, oper); numStack.push(res); // 还要把当前扫描到的符号入栈 operStack.push(ch); } else { operStack.push(ch); } } } else { operStack.push(ch); } } } else { // numStack.push(ch - 48);//ASCII 表中对比,char和int 相差48 数值1 对应的ASCII 为1, 字符'1' // 对应的ASCII 为49 // 当是连续多位数时 当发现是数时,要向后面多看一位,后面一位是符号是才入栈,否则继续扫描 keepNum += ch; if (index == expressin.length() - 1) { numStack.push(Integer.parseInt(keepNum)); } else { // 这里只是看一下,!!!! 不是index++ if (operStack.isOper(expressin.substring(index + 1, index + 2).charAt(0))) { // 如果最后一位是运算符则入栈 numStack.push(Integer.parseInt(keepNum)); // 很重要很重要!!!!! keepNum = ""; } } } index++; if (index >= expressin.length()) { break; } } while (true) { if (operStack.isEmpty()) { break; } num1 = numStack.pop(); num2 = numStack.pop(); oper = operStack.pop(); res = operStack.cal(num1, num2, oper); numStack.push(res); } System.out.println("最后的结果是:" + numStack.pop());
}
}
class ArrayStack {
private int maxSize;// 栈的大小
private int[] arr;// 用数组来模拟栈
private int top = -1;// 表是栈顶
public ArrayStack(int maxSize) {
super();
this.maxSize = maxSize;
arr = new int[maxSize];
}
// 栈满
public boolean isFull() {
return top == maxSize - 1;
}
// 栈空
public boolean isEmpty() {
return top == -1;
}
// 入栈
public void push(int value) {
// 先判断栈满了没有
if (isFull()) {
System.out.println("栈满了");
return;
}
arr[++top] = value;
}
// 出栈
public int pop() {
if (isEmpty()) {
System.out.println("栈空了");
throw new RuntimeException("栈空了");
}
return arr[top--];
}
// 查看栈顶
public int peek() {
if (isEmpty()) {
System.out.println("栈空了");
throw new RuntimeException("栈空了");
}
return arr[top];
}
public void list() {
if (isEmpty()) {
System.out.println("栈空了");
throw new RuntimeException("栈空了");
}
for (int i = top; i >= 0; i--) {
System.out.printf("栈中的元素%d\n", arr[i]);
}
}
/**
* 判断是不是一个运算符
*
* @param val
* @return
*/
public boolean isOper(char val) {
return val == '+' || val == '-' || val == '*' || val == '/' || val == '(' || val == ')';
}
public int isLeftBracket(char val) {
if (val == '(') {
return 0;
} else if (val == ')') {
return 1;
} else {
return -1;
}
}
/**
* 判断优先级 自己控制
*
* @param oper
* @return
*/
public int priority(int oper) {
if (oper == '(' || oper == ')') {
return 2;
} else if (oper == '*' || oper == '/') {
return 1;
} else if (oper == '+' || oper == '-') {
return 0;
} else {
return -1;// 表示当前只支持+ — * / 这是四种
}
}
/**
* 计算
*
* @param nmu1
* @param num2
* @param oper
* @return
*/
public int cal(int num1, int num2, int oper) {
int res = 0;
switch (oper) {
case '+':
res = num1 + num2;
break;
case '-':
res = num2 - num1;
break;
case '*':
res = num1 * num2;
break;
case '/':
res = num2 / num1;
break;
default:
break;
}
return res;
}
}
扫描二维码关注公众号,回复:
12275540 查看本文章
![](/qrcode.jpg)