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May 21, 2016 22:32
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Leetcode 236 - Lowest Common Ancestor - using List.AddRange(Stack<TreeNode>) instead of Stack.ToArray api
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using System; | |
using System.Collections.Generic; | |
using System.Linq; | |
using System.Text; | |
using System.Threading.Tasks; | |
namespace LowestCommonAncestors | |
{ | |
public class TreeNode | |
{ | |
public TreeNode left; | |
public TreeNode right; | |
public int val; | |
public TreeNode(int v) | |
{ | |
val = v; | |
} | |
} | |
/* | |
* May 21, 2016 | |
* Julia's warmup on this algorithm - C# version | |
* Tips to share: | |
* 1. Stack, always check stack is not empty before calling peek | |
* 2. Peek method is good, you can retrieve the information then decide to Pop or not | |
* 3. Try to make the design simple! | |
* 4. Stack.Array method keeps the order of iterator | |
*/ | |
class Program | |
{ | |
static void Main(string[] args) | |
{ | |
TreeNode node1 = new TreeNode(1); | |
node1.left = new TreeNode(2); | |
node1.right = new TreeNode(3); | |
node1.left.left = new TreeNode(4); | |
node1.left.right = new TreeNode(5); | |
TreeNode node = lowestCommonAncestor(node1, node1.left.left, node1.right); | |
} | |
public static TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) | |
{ | |
Stack<TreeNode> stack = new Stack<TreeNode>(); | |
TreeNode runner = root; | |
List<TreeNode> pPath = new List<TreeNode>(); | |
List<TreeNode> qPath = new List<TreeNode>(); | |
while (true) | |
{ | |
while (runner != null) | |
{ | |
stack.Push(runner); | |
if (runner == p && pPath.Count == 0) | |
{ | |
pPath.AddRange(stack); | |
} | |
if (runner == q && qPath.Count == 0) | |
{ | |
qPath.AddRange(stack); | |
} | |
if (pPath.Count > 0 && qPath.Count > 0) | |
{ | |
break; // terminate the traversal when both paths have been found | |
} | |
runner = runner.left; | |
} | |
while (stack.Count > 0 && (stack.Peek().right == null || stack.Peek().right == runner)) | |
{ | |
runner = stack.Pop(); | |
} | |
if (stack.Count == 0) | |
{ | |
break; | |
} | |
else | |
{ | |
runner = stack.Peek().right; | |
} | |
} | |
int i = 0; | |
int pStart = pPath.Count - 1; | |
int qStart = qPath.Count - 1; | |
while (pStart >= 0 && qStart >= 0 && pPath[pStart - i] == qPath[qStart - i]) | |
{ | |
++i; | |
} | |
return pPath[pStart - i + 1]; | |
} | |
} | |
} |
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