Merge pull request #235 from nutanaarohi123/Infix2Postfix

Added Infix to Postfix Conversion in Python

Author: powerexploit

Basic-Scripts/Infix_to_Postfix_Conversion/Infix_to_Postfix_Conversion.py

@@ -0,0 +1,54 @@
+# function to convert infix to postfix using array as stack
+def infix_to_postfix(infix_expression):
+    """
+    Function to change infix expression to postfix one
+    Params:
+        infix_expression: Infix Expression provided by user
+    Returns:
+        postfix_expression: Postfix Expression convertef from Infix one
+    """
+
+    # initially empty stack
+    stack = []
+    # initially empty postfix_expression
+    postfix_expression = ""
+    for char in infix_expression:
+        # if an operand then put it directly in postfix expression
+        if char not in operators:
+            postfix_expression += char
+        # else if operators should be put in stack
+        elif char == "(":
+            """append function to push
+            elements in the stack"""
+            stack.append("(")
+        elif char == ")":
+            while stack and stack[-1] != "(":
+                postfix_expression += stack.pop()
+            """ pop function to pop
+                elements from stack in LIFO order """
+            stack.pop()
+        else:
+            """if priority of char in infix_expression is less than or equal to
+            char at stack[-1] pop out and put in postfix_expression"""
+            while (
+                stack and stack[-1] != "(" and priorities[char] <= priorities[stack[-1]]
+            ):
+                postfix_expression += stack.pop()
+            stack.append(char)
+    while stack:
+        postfix_expression += stack.pop()
+    return postfix_expression
+
+
+# Set of operators
+operators = set(["+", "-", "*", "/", "(", ")", "^"])
+
+# dictionary having priorities
+priorities = {"+": 1, "-": 1, "*": 2, "/": 2, "^": 3}
+
+print("Input")
+infix_expression = input("Enter infix expression\n")
+print("Output")
+
+# Displaying the Output
+print("Postfix expression: ", infix_to_postfix(infix_expression))

Basic-Scripts/Infix_to_Postfix_Conversion/README.md

@@ -0,0 +1,27 @@
+### Infix to Postfix
+
+> • In Infix expression operator is in between every pair of operands.<br>
+> • In Postfix expression, the operator is followed for every pair of operands. 
+
+> Infix expression is converted to postfix conversion using Stack.
+> Postfix expression is evaluated using Stack in Left to Right order.
+
+##### If the scanned character is operand, show it as output. Else, If precedence of scanned operator is greater than the precedence of the operator in the stack,push it.
+
+> Else, Pop all the operators from the stack which are greater than or equal to in precedence than that of the scanned operator.
+
+•  If the scanned input is '(', push it into stack<br>
+• If the scanned input is ')' ,pop the stack and the output it until '(' comes.<br>
+• Repeat above steps. Continue Pop and output from stack until it becomes empty.
+
+##### It makes the code more efficient and even reduces the time complexity.
+### Constraints
+"""
+ Input:
+ Enter infix expression: A+C*(B^D-E)^(G+H*K)-K
+ Output:
+ Postfix expression:     ACBD^E-GHK*+^*+K-
+
+ Time Complexity : O(n)
+ Space Complexity: Θ(n)
+"""