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isUnivalTree.java
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65 lines (46 loc) · 1.26 KB
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/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
/*
Recursion: Do a DFS recursively
Time & Space: O(n)
*/
public boolean isUnivalTree(TreeNode root) {
if(root == null)
return true;
return dfs(root, root.val);
}
public boolean dfs(TreeNode node, int val){
if(node == null)
return true;
if(node.val != val)
return false;
return dfs(node.left, val) && dfs(node.right, val);
}
/*
Approach 2: Iteratively
Time and Space: O(n)
*/
public boolean isUnivalTree(TreeNode root) {
if(root == null)
return true;
Queue<TreeNode> queue = new LinkedList<>();
queue.add(root);
while(!queue.isEmpty()){
int size = queue.size();
TreeNode node = queue.remove();
if(root.val != node.val)
return false;
if(node.left != null) queue.add(node.left);
if(node.right != null) queue.add(node.right);
}
return true;
}
}