add RPN snippets

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
+}