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863-All-Nodes-Distance-K-in-Binary-Tree.java
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863-All-Nodes-Distance-K-in-Binary-Tree.java
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//Just store the value for parent values of the nodes in a map and just do bfs as we do in graph.
class Solution {
public List<Integer> distanceK(TreeNode root, TreeNode target, int k) {
HashMap<TreeNode, TreeNode> map = new HashMap<>();
//First bfs to make a mapping to the parent nodes
Queue<TreeNode> q1 = new LinkedList<>();
q1.offer(root);
while (!q1.isEmpty()) {
int size = q1.size();
for (int i = 0; i < size; i++) {
TreeNode cur = q1.poll();
if (cur.left != null) {
q1.offer(cur.left);
map.put(cur.left, cur);
}
if (cur.right != null) {
q1.offer(cur.right);
map.put(cur.right, cur);
}
}
}
//Now do the bfs
//Same as we do in graphs with a visited set
Queue<TreeNode> q2 = new LinkedList<>();
HashSet<TreeNode> vis = new HashSet<>();
List<Integer> ans = new ArrayList<>();
int dis = 0;
q2.offer(target);
while (!q2.isEmpty()) {
int size = q2.size();
for (int i = 0; i < size; i++) {
TreeNode cur = q2.poll();
if (!vis.contains(cur)) {
if (cur.left != null) q2.offer(cur.left);
if (cur.right != null) q2.offer(cur.right);
if (map.get(cur) != null) q2.offer(map.get(cur));
if (dis == k) {
ans.add(cur.val);
}
}
vis.add(cur);
}
dis++;
}
return ans;
}
}