From ba3cf0ea2ae362aadf4bb82e18802c6fb7816923 Mon Sep 17 00:00:00 2001
From: Rohit Tanwar <mst10041967@gmail.com>
Date: Tue, 2 Jan 2018 16:16:47 +0530
Subject: [PATCH] add RPN snippets

---
 snippets/infixToPostFix.md | 24 ++++++++++++++++++++++++
 snippets/postfixToInfix.md | 29 +++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)
 create mode 100644 snippets/infixToPostFix.md
 create mode 100644 snippets/postfixToInfix.md

diff --git a/snippets/infixToPostFix.md b/snippets/infixToPostFix.md
new file mode 100644
index 000000000..3fd859e37
--- /dev/null
+++ b/snippets/infixToPostFix.md
@@ -0,0 +1,24 @@
+const infix  = expr => {
+  let rpn = ''
+  let solve = expr.replace(/\^/g,'**').match(/([0-9]+|[\+\(\)\/\-]|\*+)/g).filter(el => !/\s+/.test(el) && el !== '')
+  let stack = []
+  let precedence = {'**':5,'/':4,'*':4,'+':3,'-':3}
+  solve.forEach(symbol => {
+    if(!isNaN(parseFloat(symbol)) && isFinite(symbol)){
+      rpn += symbol + ' '
+    }
+    else if (Object.keys(precedence).includes(symbol)) {
+      while(((precedence[symbol] < precedence[stack[stack.length-1]]) || ((precedence[symbol] == precedence[stack[stack.length-1]]) && symbol !== "**"))&&(stack[stack.length - 1] !== '(')) {
+        rpn += stack.pop() +  ' '
+      }
+      stack.push(symbol)
+    }
+    else if(symbol === '('){stack.push(symbol)}
+    else if(symbol === ')'){while (stack[stack.length - 1] !== '('){rpn += stack.pop() + ' '; if (stack.length === 0){throw `Mismatched parantheses`}} stack.pop()}
+    else {throw `${symbol} is not a recognized symbol`}
+  })
+  while(stack.length !== 0){
+    rpn += stack.pop() +  ' '
+  }
+  return rpn
+}
diff --git a/snippets/postfixToInfix.md b/snippets/postfixToInfix.md
new file mode 100644
index 000000000..c54bd44f0
--- /dev/null
+++ b/snippets/postfixToInfix.md
@@ -0,0 +1,29 @@
+const postFix = RPN => {
+  let convert = RPN.replace(/\^/g,'**').split(/\s+/g).filter(el => !/\s+/.test(el) && el !== '')
+  let stack = []
+  let result = []
+  let friends = {"+" : ["+","-","*","/"],"-":[],"/":["*"],"*":["/","*"],"**":["+","-","*","/"]}
+  convert.forEach(symbol => {
+    if(!isNaN(parseFloat(symbol)) && isFinite(symbol)){
+      result.push(symbol)
+    }
+    else if (Object.keys(friends).includes(symbol)) {
+      a = result.pop()
+      b = result.pop()
+      if(stack.length !==0){
+          if(friends[symbol].includes(stack.pop())){
+            result.push(`${b} ${symbol} ${a}`)
+            stack.push(symbol)
+          }
+          else{
+            result.push(`(${b}) ${symbol} ${a}`)
+            stack.push(symbol)
+          }
+      }
+      else {result.push(`${b} ${symbol} ${a}`);stack.push(symbol)}
+    }
+    else throw `${symbol} is not a recognized symbol`
+  })
+  if(result.length === 1) return result.pop()
+  else throw `${RPN} is not a correct RPN`
+}