后缀表达式

Author: LockGit

README.md

@@ -85,6 +85,16 @@ Success
 ~~~python轮子很强大~~~
 ```
 
+### rpn.py 逆波兰表达式 python 版实现
+逆波兰表达式被广泛应用于编译原理中，是一种是由波兰数学家扬·武卡谢维奇1920年引入的数学表达式方式，在逆波兰记法中，
+所有操作符置于操作数的后面，因此也被称为后缀表示法。逆波兰记法不需要括号来标识操作符的优先级。
+以利用堆栈结构减少计算机内存访问。
+➜  Py git:(master) ✗ python rpn.py
+['11111111111111', '9999999999999', '*', '99', '12', '4', '/', '-', '10', '+', '+']
+True 111111111111098888888888995 111111111111098888888888995
+True 326 326
+➜  Py git:(master) ✗
+
 
 ### dispatch.py 轮转队列
 ```

rpn.py

@@ -0,0 +1,57 @@
+# -*- coding: utf-8 -*-
+# @Author: lock
+# @Date:   2017-06-26 15:51:28
+# @Last Modified by:   lock
+# @Last Modified time: 2017-06-26 15:55:53
+def calc(s):
+    if type(s) != list:s = s.split(' ')
+    operaList = ['+', '-', '*', '/'];
+    for key, item in enumerate(s):
+        if item in operaList:
+            val = eval(s[key - 2] + item + s[key - 1])
+            s.insert(key - 2, str(val)) 
+            for x in ['1','2','3']:del s[key - 1] 
+            calc(s)
+    return sum(map(eval, s))
+def translate(calcStr):
+    element, calcList,s,stackStr,i = '', [],[],[],0
+    for key,item in enumerate(calcStr):
+        if item.isdigit():
+            element = element + item
+            if key == len(calcStr)-1:calcList.append(element)
+        else:
+            if element != '':
+                calcList.append(element)
+                element = ''
+            if item in ['+', '-', '*', '/', '(', ')']:
+                calcList.append(item)
+    calcList.insert(0,'(')
+    calcList.append(')')
+    calcList.append('#')
+    while calcList[i] != "#":
+        if (calcList[i].isdigit()):
+            stackStr.append(calcList[i])
+        elif calcList[i] == '(':
+            s.append(calcList[i])
+        elif calcList[i] == ')':
+            while s[-1] != '(':
+                stackStr.append(s.pop())
+            s.pop()
+        elif calcList[i] in ['+', '-']:
+            while s[-1] != '(':
+                stackStr.append(s.pop())
+            s.append(calcList[i])
+        elif calcList[i] in ['*', '/']:
+            while s[-1] in ['*', '/']:
+                stackStr.append(s.pop())
+            s.append(calcList[i])
+        i = i + 1
+    return stackStr
+if __name__ == '__main__':
+    s = '11111111111111*9999999999999+(99-(12/4)+10)'
+    print translate(s)
+    print str(calc(translate('11111111111111*9999999999999+(99-(12/4)+10)'))) == str(11111111111111*9999999999999+(99-(12/4)+10)),str(calc(translate(s))) , str(11111111111111*9999999999999+(99-(12/4)+10))
+    print str(calc(translate('12+1+12+33*9+4'))) == str(12+1+12+33*9+4),str(calc(translate('12+1+12+33*9+4'))) , str(12+1+12+33*9+4)
+
+
+