栈应用之中缀和后缀

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package com.dt.stactt.zhongturntohouzhui;import java.util.Stack;/** * 计算机实现转换：　　将中缀表达式转换为后缀表达式的算法思想：　　·开始扫描；　　·数字时，加入后缀表达式；　　·运算符：　　a. 若为最高级的运算符，入栈；　　b. 若为 '('，入栈；　　c. 若为 ')'，则依次把栈中的的运算符加入后缀表达式中，直到出现'('，从栈中删除'(' ；　　d. 若为不是最高级的运算符，则将从栈顶到第一个优先级不大于（小于，低于或等于）它的运算符（或 '(',但优先满足前一个条件）之间的运算符加入后缀表达式中，该运算符再入栈； * @author kuwo * */public class MidleTurnToBehind {private String testString = null;      private Stack<Character> stack = null;      public MidleTurnToBehind(String str){    this.testString = str;    stack = new Stack<Character>();    }        private void anaysisStr(){         for (int i = 0; i < testString.length(); i++) {               char c = testString.charAt(i);               if (c == '+' || c == '-') {                   if (stack.isEmpty() || stack.peek() == '(') {                       stack.push(c);                   } else {                       while (!stack.isEmpty()                               && (stack.peek() == '*' || stack.peek() == '/'                                       || stack.peek() == '+' || stack.peek() == '-')) {                           System.out.print(stack.pop());                       }                       stack.push(c);                   }               } else if (c == '*' || c == '/') {                   if (stack.isEmpty() || stack.peek() == '+'                           || stack.peek() == '-' || stack.peek() == '(') {                       stack.push(c);                   } else {                       while (!stack.isEmpty()                               && (stack.peek() == '/' || stack.peek() == '*')) {                           System.out.print(stack.pop());                       }                       stack.push(c);                   }               } else if (c == '(') {                   stack.push(c);               } else if (c == ')') {                   char temp = ' ';                   while ((temp = stack.pop()) != '(') {                       System.out.print(temp);                   }               } else {                   System.out.print(c);               }           }           if (!stack.isEmpty()) {               while (!stack.isEmpty()) {                   System.out.print(stack.pop());               }           }          }        private void anaysis(){    for (int i = 0; i < testString.length(); i++) {char c = testString.charAt(i);if(c == '+' || c == '-'){if(stack.isEmpty() || stack.peek() == '('){//当栈是空的时候，运算符可以直接入栈stack.push(c);}else{//当栈不为空的时候，就把优先级不大于（包括等于）当前运算符的内容输出while (!stack.isEmpty() && (stack.peek() == '*'|| stack.peek() == '/' || stack.peek() == '+' || stack.peek() == '-')) {System.out.print(stack.pop());}//将此运算符之前的运算符出栈，之后当前运算符就要入栈。stack.push(c);}}else if(c == '*' || c == '/'){if(stack.isEmpty() || stack.peek() == '+' || stack.peek() == '-'){stack.push(c);}else {while((!stack.isEmpty() && (stack.peek() == '/' || stack.peek() == '*'))){System.out.print(stack.pop());}stack.push(c);}}else if(c == '('){//  'c'运算符是优先级最高的运算符，只要出现这个运算符就要入栈stack.push(c);}else if(c == ')'){//如果出现了')'运算符则要把'（'运算符之后的所以的运算符出栈char temp;while ((temp = stack.peek()) != '(') {System.out.print(temp);}}else{//如果当前字符不是运算符，则直接输出System.out.print(c);}}         if (!stack.isEmpty()) {               while (!stack.isEmpty()) {                   System.out.print(stack.pop());               }           }          }        public static void main(String[] args) {  //    MidleTurnToBehind testStacknew = new MidleTurnToBehind("A+B*(C-D)/E+F/H");  //    MidleTurnToBehind testStacknew = new MidleTurnToBehind("a+b*c+(d*e+f)*g");      MidleTurnToBehind testStacknew = new MidleTurnToBehind("a-b-c");  //    MidleTurnToBehind testStacknew = new MidleTurnToBehind("ac");  //        testStacknew.anaysisStr();          testStacknew.anaysis();      }    }
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