queueUsingStacks.ts

// Queue using two stacks

function createDoubleStackQueue() {
  var that = {};
  var pushContainer = [];
  var popContainer = [];
  
  function moveElementToPopContainer() {
      while (pushContainer.length !==0 ) {
          var element = pushContainer.pop();
          popContainer.push(element);
      }
  }
  
  that.push = function(element) {
      pushContainer.push(element);
  };
  
  that.shift = function() {
      if (popContainer.length === 0) {
          moveElementToPopContainer();
      }
      if (popContainer.length === 0) {
          return null;
      } else {
          return popContainer.pop();
      }
  };
  
  that.front = function() {
      if (popContainer.length === 0) {
          moveElementToPopContainer();
      }
      if (popContainer.length === 0) {
          return null;
      }
      return popContainer[popContainer.length - 1];
  };
  
  that.length = function() {
      return pushContainer.length + popContainer.length;
  };
  
  that.isEmpty = function() {
      return (pushContainer.length + popContainer.length) === 0;
  };
  
  return that;
}