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Program.cs
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Program.cs
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using System;
using System.Collections.Generic;
namespace ClosestLeafInABinaryTree
{
public class TreeNode
{
public int val;
public TreeNode left;
public TreeNode right;
public TreeNode(int val = 0, TreeNode left = null, TreeNode right = null)
{
this.val = val;
this.left = left;
this.right = right;
}
}
class Program
{
static void Main(string[] args)
{
var a = new TreeNode(1);
var b = new TreeNode(2);
var c = new TreeNode(3);
var d = new TreeNode(4);
var e = new TreeNode(5);
var f = new TreeNode(6);
a.left = b;
a.right = c;
b.left = d;
d.left = e;
e.left = f;
int k = 5;
Console.WriteLine();
}
public int FindClosestLeaf(TreeNode root, int k)
{
var graph = new Dictionary<TreeNode, List<TreeNode>>();
var leaves = new List<TreeNode>();
var parent = new TreeNode(0, root);
DFS(graph, leaves, root, parent);
int path = int.MaxValue, res = 0;
foreach (var leaf in leaves)
{
var visit = new HashSet<TreeNode> {leaf};
var queue = new Queue<TreeNode>();
queue.Enqueue(leaf);
var layer = 0;
while (queue.Count != 0)
{
var count = queue.Count;
layer++;
for (int i = 0; i < count; i++)
{
var cur = queue.Dequeue();
if (cur.val == k)
{
if (layer < path)
{
path = layer;
res = leaf.val;
}
break;
}
foreach (var next in graph[cur])
{
if(visit.Add(next))
queue.Enqueue(next);
}
}
}
}
return res;
}
static void DFS(Dictionary<TreeNode, List<TreeNode>> graph, List<TreeNode> leaves, TreeNode node, TreeNode parent)
{
if(node == null) return;
if (node.left == node.right) leaves.Add(node);
if(!graph.ContainsKey(node))
graph[node] = new List<TreeNode>();
if(!graph.ContainsKey(parent))
graph[parent] = new List<TreeNode>();
graph[node].Add(parent);
graph[parent].Add(node);
DFS(graph, leaves, node.left, node);
DFS(graph, leaves, node.right, node);
}
}
}