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smallestSubtree.java
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51 lines (49 loc) · 1.71 KB
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import java.util.*;
public class smallestSubtree {
public static void main(String[] args){
Codec obj = new Codec();
String data = "6,2,8,0,4,7,9,N,N,3,5,N,N,N,N,N,N,N,N,";
TreeNode root = obj.deserilize2(data);
TreeNode lca = subtreeWithAllDeepest(root);
System.out.println(lca.val);
}
/*
method 1: BFS + Lowest Common Ancestor
method 2: dfs (discuss 里面大佬说的) 学习一下
* */
public static TreeNode subtreeWithAllDeepest(TreeNode root) {
Map<TreeNode, TreeNode> parents = new HashMap<>();
// step 1: find deepest nodes
Queue<TreeNode> queue = new LinkedList<>();
List<TreeNode> deepest = new ArrayList<>();
queue.add(root);
while(!queue.isEmpty()){
int size = queue.size();
List<TreeNode> curLevel = new ArrayList<>();
for(int i = 0; i < size; i ++){
TreeNode cur = queue.remove();
curLevel.add(cur);
if(cur.left != null) {
queue.add(cur.left);
parents.put(cur.left, cur);
}
if(cur.right != null) {
queue.add(cur.right);
parents.put(cur.right, cur);
}
}
deepest = new ArrayList<>(curLevel);
}
// step 2: find lowest common ancestor
Set<TreeNode> set = new HashSet<>(deepest);
List<TreeNode> prev = new ArrayList<>();
while(set.size() > 1){
prev = new ArrayList<>();
for(TreeNode cur : set){
prev.add(parents.get(cur));
}
set = new HashSet<>(prev);
}
return prev.get(0);
}
}