//----------------------------------------------------------------------------------
// Iteration using Queue
public static IList<IList<int>> LevelOrderIteration(TreeNode root)
{
IList<IList<int>> res = new List<IList<int>>();
if (root == null)
return res;
Queue<TreeNode> queue = new Queue<TreeNode>();
queue.Enqueue(root);
int expect = 1; // total number of nodes in current level
int visit = 0; // number of visited nodes in current level
IList<int> level = new List<int>(); // current level
while (queue.Count != 0)
{
TreeNode curr = queue.Dequeue();
level.Add(curr.val);
visit++;
if (curr.left != null)
queue.Enqueue(curr.left);
if (curr.right != null)
queue.Enqueue(curr.right);
if (visit == expect)
{
expect = queue.Count;
visit = 0;
res.Add(level);
level = new List<int>();
}
}
return res;
}
public static int GetClosestValue(TreeNode root, double target)
{
if ((double)root.val == target) return root.val;
TreeNode child = target < root.val ? root.left : root.right;
if (child == null) return root.val;
int temp = GetClosestValue(child, target);
return Math.Abs(temp - target) < Math.Abs(root.val - target) ? temp : root.val;
}
// return the max path sum starting from root
// and update the global max during process
private int DFS(TreeNode root)
{
if (root == null) return 0;
// ignore children path with negative sum
int leftPath = Math.Max(0, DFS(root.left)); // simple path rooting at left child
int rightPath = Math.Max(0, DFS(root.right)); // simple path rooting at right child
maxSum = Math.Max(maxSum, leftPath + rightPath + root.val);
return Math.Max(leftPath, rightPath) + root.val;
}
private void DFS(TreeNode root, int pathSum)
{
if (root == null) return;
if (root.left == null && root.right == null)
{
treeSum += pathSum * 10 + root.val;
return;
}
pathSum = pathSum * 10 + root.val;
DFS(root.left, pathSum);
DFS(root.right, pathSum);
}
// Question: #103
public static IList<IList<int>> ZigzagTraverse(TreeNode root)
{
if (root == null) return new List<IList<int>>();
IList<IList<int>> res = new List<IList<int>>();
// for nodes in odd level
Stack<TreeNode> oddStack = new Stack<TreeNode>();
// for nodes in even level
Stack<TreeNode> evenStack = new Stack<TreeNode>();
oddStack.Push(root);
while (oddStack.Count != 0 || evenStack.Count != 0)
{
IList<int> level = new List<int>();
while (oddStack.Count != 0)
{
TreeNode odd = oddStack.Pop();
level.Add(odd.val);
if (odd.left != null)
{
evenStack.Push(odd.left);
}
if (odd.right != null)
{
evenStack.Push(odd.right);
}
}
if (level.Count != 0)
{
res.Add(level);
level = new List<int>();
}
while (evenStack.Count != 0)
{
TreeNode even = evenStack.Pop();
level.Add(even.val);
if (even.right != null)
{
oddStack.Push(even.right);
}
if (even.left != null)
{
oddStack.Push(even.left);
}
}
if (level.Count != 0)
{
res.Add(level);
}
}
return res;
}
private static void DFS(TreeNode p, IList<IList<int>> res, int level)
{
if (p == null) return;
if (res.Count <= level)
{
IList<int> newLevel = new List<int>();
res.Add(newLevel);
}
IList<int> curr = res[level];
curr.Add(p.val);
DFS(p.left, res, level + 1);
DFS(p.right, res, level + 1);
}
public static IList<IList<int>> LevelOrderBottom(TreeNode root)
{
IList<IList<int>> res = new List<IList<int>>();
DFS(root, res, 0);
// reverse
int mid = res.Count / 2;
for (int i = 0; i < mid; i++)
{
IList<int> temp = res[i];
res[i] = res[res.Count - i - 1];
res[res.Count - i - 1] = temp;
}
return res;
}
private void DFS(TreeNode root, StringBuilder path)
{
if (root == null) return;
if (path.Length > 0)
{
path.Append("->");
}
path.Append(root.val);
if (root.left == null && root.right == null)
{
res.Add(path.ToString());
}
DFS(root.left, new StringBuilder(path.ToString()));
DFS(root.right, new StringBuilder(path.ToString()));
}
private bool DFS(TreeNode root, int pathRemain)
{
if (root == null) return false;
// leaf node
if (root.left == null && root.right == null)
{
if (root.val == pathRemain)
{
return true;
}
return false;
}
pathRemain -= root.val;
return DFS(root.left, pathRemain) || DFS(root.right, pathRemain);
}
public TreeNode GetLowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q)
{
if (root == null)
return root;
if (p == null || q == null)
return root;
if (p == root || q == root)
return root;
if ((p.val < root.val && q.val > root.val)
|| (p.val > root.val && q.val < root.val))
return root;
if (p.val < root.val && q.val < root.val)
{
return GetLowestCommonAncestor(root.left, p, q);
}
else
{
return GetLowestCommonAncestor(root.right, p, q);
}
}
public IList<string> BinaryTreePaths(TreeNode root)
{
DFS(root, new StringBuilder());
return res;
}
public int SumNumbers(TreeNode root)
{
DFS(root, 0);
return treeSum;
}
public bool HasPathSum(TreeNode root, int sum)
{
return DFS(root, sum);
}
// Recursion using DFS
public static IList<IList<int>> LevelOrder(TreeNode root)
{
IList<IList<int>> res = new List<IList<int>>();
DFS(root, res, 0);
return res;
}
public int MaxPathSum(TreeNode root)
{
DFS(root);
return maxSum;
}
//-------------------------------------------------------------------------------------------------
// O(n) space method
// using extra space with queue and stack
public static List<int> TraverseWithSimpleNode(TreeNode root) {
if (root == null) return new List<int>();
List<int> res = new List<int>();
Queue<TreeNode> queue = new Queue<TreeNode>();
Stack<TreeNode> stack = new Stack<TreeNode>();
stack.Push(root);
while (stack.Count != 0 || queue.Count != 0) {
while (stack.Count != 0) {
TreeNode p = stack.Pop();
res.Add(p.val);
if (p.left != null) queue.Enqueue(p.left);
if (p.right != null) queue.Enqueue(p.right);
}
while (queue.Count != 0) {
TreeNode q = queue.Dequeue();
res.Add(q.val);
if (q.left != null) stack.Push(q.left);
if (q.right != null) stack.Push(q.right);
}
}
return res;
}
private int Height(TreeNode root)
{
if (root == null) return 0;
return Math.Max(Height(root.left), Height(root.right)) + 1;
}
/*
* #110
*/
public bool IsBalanced(TreeNode root)
{
if (root == null) return true;
return IsBalanced(root.left) && IsBalanced(root.right) && Math.Abs(Height(root.left) - Height(root.right)) < 2;
}