101. Symmetric Tree

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LeetCode

Rrecursion

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class Solution {
    private boolean isMirror(TreeNode t1,TreeNode t2){
        if(t1==null && t2==null) return true;
        if(t1==null || t2==null) return false;
        return t1.val==t2.val&&isMirror(t1.left,t2.right)&&isMirror(t1.right,t2.left);
    }
    public boolean isSymmetric(TreeNode root) {
        return isMirror(root,root);
    }
}

Iteration: BFS

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class Solution {
    public boolean isSymmetric(TreeNode root) {
        LinkedList<TreeNode> queue=new LinkedList<>();
        queue.push(root);
        queue.push(root);
        while(!queue.isEmpty()){
            TreeNode t1=queue.poll();
            TreeNode t2=queue.poll();
            if(t1==null && t2==null) continue;
            if(t1==null || t2==null) return false;
            if(t1.val!=t2.val) return false;
            queue.push(t1.left);
            queue.push(t2.right);
            queue.push(t1.right);
            queue.push(t2.left);
        }
        return true;
    }
}

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