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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DFS
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| class Solution {
public TreeNode mergeTrees(TreeNode root1, TreeNode root2) {
if (root1 == null && root2 == null) {
return null;
}
TreeNode root = new TreeNode();
if (root1 != null) {
root.val += root1.val;
}
if (root2 != null) {
root.val += root2.val;
}
root.left = mergeTrees(root1 == null ? null : root1.left, root2 == null ? null : root2.left);
root.right = mergeTrees(root1 == null ? null : root1.right, root2 == null ? null : root2.right);
return root;
}
}
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BFS
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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;
}
}
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References
617. Merge Two Binary Trees