private static void RunStackTest()
{
Console.WriteLine("Start");
Console.WriteLine("Push 1");
var stack = new Stack(1);
Console.WriteLine("Push 2");
stack.Push(2);
Console.WriteLine("Push 3");
stack.Push(3);
Console.WriteLine("Push 4");
stack.Push(4);
Console.WriteLine("Pop " + stack.Pop());
Console.WriteLine("Pop " + stack.Pop());
Console.WriteLine("Pop " + stack.Pop());
Console.WriteLine("Pop " + stack.Pop());
Console.WriteLine("Pop ??????? expected Exception");
try
{
stack.Pop();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
Console.WriteLine("Push 5 on Empty stack");
stack.Push(5);
Console.WriteLine("Pop " + stack.Pop());
}
//DFS
public static bool ExistsPath(Graph<int> graph, int start, int destination)
{
var nodes = graph.Nodes;
foreach (var node in nodes)
{
node.NodeState=State.Unvisted;
}
var discovered = new Stack<Node<int>>();
var currentNode = graph.FindNode(start);
currentNode.NodeState = State.Visited;
discovered.Push(currentNode);
while (discovered.Count>0)
{
currentNode = discovered.Pop();
foreach (var node in currentNode.Neighbors)
{
if (node.NodeState.Equals(State.Unvisted))
{
node.NodeState=State.Visited;
discovered.Push(node);
}
}
}
return graph.FindNode(destination).NodeState.Equals(State.Visited);
}
public void Adding_Items_In_Descending_Order_Then_Popping_Sets_Minimum_To_Previous_Minimum_Value()
{
DataStructures.Stack stack = new DataStructures.Stack();
stack.Push(5);
stack.Push(4);
stack.Push(3);
stack.Push(2);
stack.Push(1);
stack.Pop();
Assert.AreEqual(2, stack.GetMinimumItem());
}
//---------------------------------------------------------------------
//------------- D F S + I T E R A T I V E -------------------
//---------------------------------------------------------------------
//DFS: 先序 Pre-order Traversal, Stack
public List<int> PreOrderTraversal_Iterative1(TreeNode root)
{
List<int> result = new List<int>();
Stack<TreeNode> stack = new Stack<TreeNode>();
stack.Push(root);
while (stack.Count != 0)
{
root = stack.Pop();
if (root != null)
{
result.Add(root.val);
//Prevent pushing null node to enhance performance.
if (root.right != null) stack.Push(root.right);
if (root.left != null) stack.Push(root.left);
}
}
return result;
}
//DFS: 先序 Pre-order Traversal, Stack
public List<int> PreOrderTraversal_Iterative2(TreeNode root)
{
List<int> result = new List<int>();
Stack<TreeNode> stack = new Stack<TreeNode>();
while (root != null || stack.Count != 0)
{
if (root != null)
{
//Store root value first.
result.Add(root.val);
//Push right child into stack
stack.Push(root.right);
//Iterate left child first.
root = root.left;
}
else
{
//if left child does not exist anymore, iterate the nearest right child.
root = stack.Pop();
}
}
return result;
}
//DFS: 后序 Post-order Traversal, (Reversed Pre-order Traversal)
public List<int> PostOrderTraversal_Iterative2(TreeNode root)
{
List<int> result = new List<int>();
//Iterative: Reverse Pre-Order Traversal.
Stack<TreeNode> stack = new Stack<TreeNode>();
while (root != null || stack.Count != 0)
{
if (root != null)
{
result.Add(root.val);
if (root.left != null) stack.Push(root.left);
root = root.right;
}
else
{
root = stack.Pop();
}
}
result.Reverse();
return result;
}
//DFS: 后序 Post-order Traversal, Stack
public List<int> PostOrderTraversal_Iterative1(TreeNode root)
{
//Postorder traversal is more complicated to implement comparing to Preorder and Inorder.
//At what point shall we visit the root node:
//Condition 1: The root node has no child at all.
//Condition 2: The root's child has already been visited.
List<int> result = new List<int>();
Stack<TreeNode> stack = new Stack<TreeNode>();
if (root != null)
stack.Push(root);
TreeNode prev = null;
while (stack.Count != 0)
{
root = stack.Peek();
bool noChild = (root.left == null && root.right == null);
bool doneChild = false;
if (prev != null && (prev == root.left || prev == root.right))
doneChild = true;
//直到没有child了或者child已经访问完了才把栈顶元素出栈
if (noChild || doneChild)
{
root = stack.Pop();
result.Add(root.val);
prev = root;
}
else
{
if (root.right != null)
stack.Push(root.right);
if (root.left != null)
stack.Push(root.left);
}
}
return result;
}
//DFS: 中序 In-order Traversal, Stack
public List<int> InOrderTraversal_Iterative1(TreeNode root)
{
//Step 1: Iterate left subtree, push left node into stack.
//Step 2: Stop push until node is null (its parent has no left child).
//Step 3: Pop current node, store the value.
//Step 4: Switch to the right subtree and iterate right subtree,
List<int> result = new List<int>();
Stack<TreeNode> stack = new Stack<TreeNode>();
//Stop loop when both root is null and stack is empty.
while (root != null || stack.Count != 0)
{
if (root != null)
{
//Store root for later use
stack.Push(root);
//Iterate left child first.
root = root.left;
}
else
{
//If left child does not exist anymore, extract its parent
root = stack.Pop();
//And store parent value
result.Add(root.val);
//Then iterate its right child.
root = root.right;
}
}
return result;
}
public int solution(string S)
{
int minInteger = 0;
int maxInteger = (1 << 20) - 1;
Stack<int> stack = new Stack<int>();
foreach (string op in S.Split(' '))
{
if (op == "DUP")
{
if (!stack.Any())
{
return -1;
}
stack.Push(stack.Peek());
}
else if (op == "POP")
{
if (!stack.Any())
{
return -1;
}
stack.Pop();
}
else if (op == "+")
{
if (stack.Count() < 2)
{
return -1;
}
var top = stack.Pop();
var nextTop = stack.Pop();
var sum = top + nextTop;
if (sum > maxInteger)
{
// Overflow
return -1;
}
stack.Push(sum);
}
else if (op == "-")
{
if (stack.Count() < 2)
{
return -1;
}
var top = stack.Pop();
var nextTop = stack.Pop();
var diff = top - nextTop;
if (diff < minInteger)
{
// Overflow
return -1;
}
stack.Push(diff);
}
else
{
int number;
if (!int.TryParse(op, out number))
{
return -1;
}
if (number < minInteger || number > maxInteger)
{
return -1;
}
stack.Push(number);
}
}
if (!stack.Any())
{
return -1;
}
return stack.Pop();
}