(attempt) 3.3 - 3.5

Author: Tony K Tan

lib/chapter3/3.3 - Stack of Plates/stackOfPlates.js

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+var SetOfStacks = function(capacity) {
+  // implement as an array of stacks
+  this.capacity = capacity;
+  this.stackSet = [];
+};
+
+SetOfStacks.prototype.push = function(value) {
+  if (this.stackSet.length === 0  || this.stackSet[this.stackSet.length - 1].length === this.capacity) {
+    var newStack = [];
+    newStack.push(value);
+    this.stackSet.push(newStack);
+  } else {
+    this.stackSet[this.stackSet.length - 1].push(value);
+  }
+};
+
+SetOfStacks.prototype.pop = function() {
+  if (this.numStack === 0) {
+    return undefined;
+  } else if (this.stackSet[this.stackSet.length - 1].length === 0) {
+    this.stackSet.pop();
+  } 
+  return this.stackSet[this.stackSet.length - 1].pop();
+};
+
+SetOfStacks.prototype.peek = function() {
+  var currStack = this.stackSet[this.stackSet.length - 1];
+  return currStack[currStack.length - 1];
+};
+
+SetOfStacks.prototype.isEmpty = function() {
+  return this.stackSet.length === 0;
+};
+
+SetOfStacks.prototype.popAt = function(index) {
+  return this.stackSet[index].pop();
+};
+
+/* TESTS */
+
+var s = new SetOfStacks(3);
+s.push(1);
+s.push(2);
+s.push(3);
+s.push(4);
+s.push(5);
+s.push(6);
+s.push(7);
+s.push(8);
+s.push(9);
+s.push(10);
+s.push(11);
+s.push(12);
+s.push(13);
+s.push(14);
+
+console.log(s.stackSet);
+
+s.popAt(2);
+
+console.log(s.stackSet);
+
+s.pop();
+s.pop();
+s.pop();
+s.pop();
+s.pop();
+s.pop();
+s.pop();
+s.pop();
+s.pop();
+
+console.log(s.stackSet);
+
+
+// Note: if stack not implemented as an array, would need to separately keep track of the depth 
+// of each stack in an array

lib/chapter3/3.4 - Queue via Stacks/queueViaStacks.js

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+var Stack = require('./../util/Stack');
+
+var myQueue = function() {
+  this.front = new Stack();
+  this.back = new Stack();
+  this.backUp = true;
+};
+
+myQueue.prototype.add = function(value) {
+  if (!this.backUp) {
+    while (!this.front.isEmpty()) {
+      this.back.push(this.front.pop());
+    }
+    this.backUp = true;
+  }
+  this.back.push(value);
+};
+
+myQueue.prototype.remove = function() {
+  if (this.backUp) {
+    while(!this.back.isEmpty()) {
+      this.front.push(this.back.pop());
+    }
+    this.backUp = false;
+  }
+  return this.front.pop();
+};
+
+myQueue.prototype.peek = function() {
+  if (this.backUp) {
+    while(!this.back.isEmpty()) {
+      this.front.push(this.back.pop());
+    }
+    this.backUp = false;
+  }
+  return this.front.peek();
+};
+
+myQueue.prototype.isEmpty = function() {
+  return this.front.isEmpty() && this.back.isEmpty();
+};
+
+/* TEST */
+var m = new myQueue();
+console.log(m.isEmpty(), true);
+
+m.add('a');
+m.add('b');
+m.add('c');
+m.add('d');
+m.add('e');
+m.remove();
+console.log(m.peek(), 'b');

lib/chapter3/3.5 - Sort Stack/sortStack.js

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+var Stack = require('./../util/Stack');
+
+var sortStack = function(stack) {
+  var tempStack = new Stack();
+  var currMin = Infinity;
+  var stackDepth = 0;
+  
+  while (!stack.isEmpty()) {
+    if (stack.peek() <= currMin) {
+      if (currMin !== Infinity) {
+        tempStack.push(currMin);      
+      }
+      currMin = stack.pop();
+    } else {
+      tempStack.push(stack.pop());
+    }
+    stackDepth++;
+  }
+
+  while (!tempStack.isEmpty()) {
+    stack.push(tempStack.pop());
+  }
+
+  tempStack.push(currMin);
+  currMin = Infinity;
+  stackDepth--;
+
+  while (stackDepth > 0) {
+
+    while (!stack.isEmpty()) {
+      if (stack.peek() <= currMin) {
+        if (currMin !== Infinity) {
+          tempStack.push(currMin);
+        }
+        currMin = stack.pop();
+      } else {
+        tempStack.push(stack.pop());
+      }
+    }
+
+    for (var i = 0; i < stackDepth - 1; i++) {
+      stack.push(tempStack.pop());
+    }
+
+    tempStack.push(currMin);
+    currMin = Infinity;
+    stackDepth--;
+  }
+
+  while (!tempStack.isEmpty()) {
+    stack.push(tempStack.pop());
+  }
+
+  return stack;
+};
+
+/* TEST */
+var s = new Stack();
+s.push(99);
+s.push(4);
+s.push(1);
+s.push(6);
+s.push(8);
+s.push(10);
+s.push(22);
+s.push(3);
+s.push(72);
+
+var sortS = sortStack(s);
+
+while (!sortS.isEmpty()) {
+  console.log(sortS.pop());
+}
+
+
+