Complete balancedParens.js

balancedParens/balancedParens.js

@@ -25,5 +25,35 @@
  */
 
 var balancedParens = function (input) {
+  var stack = [];
+  var map = {
+    ')' : '(',
+    ']' : '[',
+    '}' : '{'
+  };
+  var length = input.length;
+  var i, currentChar, popped;
 
+  for (i = 0; i < length; i += 1) {
+    currentChar = input[i];
+
+    if ( isOpening(currentChar) ) {
+      stack.push( currentChar );
+    } else if ( isClosing(currentChar) ) {
+      popped = stack.pop();
+      if ( map[currentChar] !== popped ) {
+        return false;
+      }
+    }
+  }
+
+  return stack.length === 0;
+};
+
+var isOpening = function (char) {
+  return char === '(' || char === '[' || char === '{';
+};
+
+var isClosing = function (char) {
+  return char === ')' || char === ']' || char === '}';
 };