From 3f1d2c5ed4f06c09bb1c6a9e3fe71078b0fd35a6 Mon Sep 17 00:00:00 2001
From: IzanBF <izanbf1803@gmail.com>
Date: Sat, 29 Apr 2017 02:14:27 +0200
Subject: [PATCH] Added calculator/math_parser.py full code

---
 README.md                 |   3 +-
 calculator/math_parser.py | 117 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 119 insertions(+), 1 deletion(-)
 create mode 100644 calculator/math_parser.py

diff --git a/README.md b/README.md
index c21bd8abc..24998877d 100644
--- a/README.md
+++ b/README.md
@@ -45,6 +45,8 @@ Minimal and clean example implementations of data structures and algorithms in P
     - [single_number](bit/single_number.py)
     - [subsets](bit/subsets.py)
     - [add_without_operator](bit/add_without_operator.py)
+- [calculator](calculator)
+    - [math_parser](calculator/math_parser.py)
 - [dfs](dfs)
     - [all_factors](dfs/all_factors.py)
     - [count_islands](dfs/count_islands.py)
@@ -200,7 +202,6 @@ Minimal and clean example implementations of data structures and algorithms in P
 - [design](design)
     - [alarm_system](design/alarm_system.md)
     - [all_o_one_ds](design/all_o_one_ds.md)
-    - [calculator](design/calculator.md)
     - [excel_table](design/excel_table.md)
     - [LRUcache](design/LRUcache.md)
     - [nearby_drivers](design/nearby_drivers.md)
diff --git a/calculator/math_parser.py b/calculator/math_parser.py
new file mode 100644
index 000000000..2955c576f
--- /dev/null
+++ b/calculator/math_parser.py
@@ -0,0 +1,117 @@
+"""
+Contributed by izanbf1803.
+
+Example:
+-------------------------------------------------------------------------------------------------
+	Code:
+		|	exp = "2452 * (3 * 6 + 1) * 6 / 235"
+		|	print("Expression:", exp)
+		|	print("Parsed expression:", mp.parse(exp))
+		|	print("Evaluation result:", mp.evaluate(exp))
+
+	Output:
+		|	Expression: 2452 * (3 * 6 + 1) * 6 / 235
+		|	Parsed expression: ['2452', '*', '(', '3', '*', '6', '+', '1', ')', '*', '6', '/', '235']
+		|	Evaluation result: 1189.4808510638297
+-------------------------------------------------------------------------------------------------
+"""
+
+from collections import deque
+
+__operators__ = "+-/*"
+__parenthesis__ = "()"
+__priority__ = {
+	'+': 0,
+	'-': 0,
+	'*': 1,
+	'/': 1,
+}
+
+def isOperator(token):
+	"""
+	Check if token it's a operator
+
+	token Char: Token
+	"""
+	return token in __operators__
+
+def higherPriority(op1, op2):
+	"""
+	Check if op1 have higher priority than op2
+
+	op1 Char: Operation Token 1
+	op2 Char: Operation Token 2
+	"""
+	return __priority__[op1] >= __priority__[op2]
+
+def calc(n2, n1, operator):
+	"""
+	Calculate operation result
+
+	n2 Number: Number 2
+	n1 Number: Number 1
+	operator Char: Operation to calculate
+	"""
+	if operator == '-': return n1 - n2
+	elif operator == '+': return n1 + n2
+	elif operator == '*': return n1 * n2
+	elif operator == '/': return n1 / n2
+	return 0
+
+def applyOperation(opStack, outStack):
+	"""
+	Apply operation to the first 2 items of the output queue
+
+	opStack Deque (reference)
+	outStack Deque (reference)
+	"""
+	outStack.append(calc(outStack.pop(), outStack.pop(), opStack.pop()))
+
+def parse(expression):
+	"""
+	Return array of parsed tokens in the expression
+
+	expression String: Math expression to parse in infix notation
+	"""
+	result = []
+	current = ""
+	for i in expression:
+		if i.isdigit():
+			current += i
+		else:
+			if len(current) > 0:
+				result.append(current)
+				current = ""
+			if i != ' ':
+				result.append(i)
+	if len(current) > 0:
+		result.append(current)
+	return result
+
+def evaluate(expression):
+	"""
+	Calculate result of expression
+
+	expression String: The expression
+	type Type (optional): Number type [int, float]
+	"""
+	opStack  = deque() # operator stack
+	outStack = deque() # output stack (values)
+	for token in parse(expression):
+		if token.isdigit():
+			outStack.append(float(token))
+		elif token == '(':
+			opStack.append(token)
+		elif token == ')':
+			while len(opStack) > 0 and opStack[-1] != '(':
+				applyOperation(opStack, outStack)
+			opStack.pop() # Remove remaining '('
+		else: # isOperator(token)
+			while len(opStack) > 0 and isOperator(opStack[-1]) and higherPriority(opStack[-1], token):
+				applyOperation(opStack, outStack)
+			opStack.append(token)
+
+	while len(opStack) > 0:
+		applyOperation(opStack, outStack)
+
+	return outStack[-1]
\ No newline at end of file