100. Same
TreeGiven two binary trees, write a function to check if they are the same or not.
Two binary trees are considered the same if they are structurally identical and the nodes have the same value.
Example 1:
Input: 1 1
/ \ /
2 3 2 3
[1,2,3], [1,2,3]
Output: true
class Solution {
// recrusion
public boolean isSameTree(TreeNode p, TreeNode q) {
if (p == null && q == null) return true;
if (p == null && q != null || p != null && q == null) return false;
if(p.val == q.val){
return isSameTree(p.left,q.left)&& isSameTree(p.right,q.right);
}
else return false;
}
}
101. Symmetric Tree
Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
For example, this binary tree [1,2,2,3,4,4,3] is symmetric:
class Solution {
// recrusion
public boolean isSymmetric(TreeNode root) {
return root==null || Symmetric(root.left,root.right);
}
private boolean Symmetric(TreeNode left, TreeNode right)
{
if (left == null || right == null) return left == right;
if(left.val ==right.val)
return Symmetric(left.left,right.right)&& Symmetric(left.right,right.left);
else return false;
}
}
class Solution {
//iteration
public boolean isSymmetric(TreeNode root)
{
if(root==null) return true;
Stack<TreeNode> stack = new Stack<TreeNode> ();
stack.push(root.left);
stack.push(root.right);
while(!stack.isEmpty())
{
TreeNode right = stack.pop();
TreeNode left = stack.pop();
if(left==null && right ==null) continue;
if(left == null|| right== null || left.val!= right.val) return false;
stack.push(left.left);
stack.push(right.right);
stack.push(left.right);
stack.push(right.left);
}
return true;
}
}