package exercise.stack;
/**
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Infix expression
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When the left parenthesis is encountered, it is placed directly on the operator stack, ... when the right parenthesis is encountered, if the top of the current operator stack is not a left parenthesis, one operator and two operands will be exited until the top of the operator stack is the left parenthesis paired with the right parenthesis. At this time the left parenthesis can be popped out of the stack
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@ClassName: NifixExpression
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@author: fan
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@date: June 12, 2020 11:18:53 AM
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@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;// The size of the stack private int[] arr;// Use an array to simulate the stack private int top = -1;// The table is the top of the stack
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;
}
}