100. Same Tree

,

DFS

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class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null && q == null) {
            return true;
        } else if (p != null && q != null) {
            return p.val == q.val && isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
        } else {
            return false;
        }
    }
}

BFS

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class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null && q == null) {
            return true;
        } else if (p != null ^ q != null) {
            return false;
        }

        Queue<TreeNode> queueA = new LinkedList<>();
        Queue<TreeNode> queueB = new LinkedList<>();
        queueA.offer(p);
        queueB.offer(q);

        while (!queueA.isEmpty() && !queueB.isEmpty()) {
            TreeNode nodeA = queueA.poll();
            TreeNode nodeB = queueB.poll();

            if (nodeA.val != nodeB.val) {
                return false;
            }

            if (nodeA.left != null ^ nodeB.left != null) {
                return false;
            }
            if (nodeA.left != null) {
                queueA.offer(nodeA.left);
                queueB.offer(nodeB.left);
            }

            if (nodeA.right != null ^ nodeB.right != null) {
                return false;
            }
            if (nodeB.right != null) {
                queueA.offer(nodeA.right);
                queueB.offer(nodeB.right);
            }
        }

        return queueA.isEmpty() && queueB.isEmpty();
    }
}

References

100. Same Tree