Poison

617. Merge Two Binary Trees

发表于
DFS
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class Solution {
    public TreeNode mergeTrees(TreeNode root1, TreeNode root2) {
        if (root1 == null) {
            return root2;
        } else if (root2 == null) {
            return root1;
        }

        TreeNode root = new TreeNode(root1.val + root2.val);
        root.left = mergeTrees(root1.left, root2.left);
        root.right = mergeTrees(root1.right, root2.right);

        return root;
    }
}
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class Solution {
    public TreeNode mergeTrees(TreeNode root1, TreeNode root2) {
        if (root1 == null) {
            return root2;
        } else if (root2 == null) {
            return root1;
        }

        TreeNode node = new TreeNode(root1.val + root2.val);
        Queue<TreeNode> queue = new LinkedList<>();
        Queue<TreeNode> queue1 = new LinkedList<>();
        Queue<TreeNode> queue2 = new LinkedList<>();
        queue.add(node);
        queue1.add(root1);
        queue2.add(root2);

        while (!queue1.isEmpty() && !queue2.isEmpty()) {
            TreeNode mergedRoot = queue.poll(), leftRoot = queue1.poll(), rightRoot = queue2.poll();
            TreeNode left1 = leftRoot.left, right1 = leftRoot.right;
            TreeNode left2 = rightRoot.left, right2 = rightRoot.right;

            if (left1 != null || left2 != null) {
                if (left1 != null && left2 != null) {
                    TreeNode left = new TreeNode(left1.val + left2.val);
                    mergedRoot.left = left;
                    queue.add(left);
                    queue1.add(left1);
                    queue2.add(left2);
                } else if (left1 != null) {
                    mergedRoot.left = left1;
                } else if (left2 != null) {
                    mergedRoot.left = left2;
                }
            }

            if (right1 != null || right2 != null) {
                if (right1 != null && right2 != null) {
                    TreeNode right = new TreeNode(right1.val + right2.val);
                    mergedRoot.right = right;
                    queue.add(right);
                    queue1.add(right1);
                    queue2.add(right2);
                } else if (right1 != null) {
                    mergedRoot.right = right1;
                } else if (right2 != null) {
                    mergedRoot.right = right2;
                }

            }
        }

        return node;
    }
}
Reference

617. Merge Two Binary Trees