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This approach utilizes recursion to traverse both trees simultaneously. If both node values are non-null, we sum them up as the new value and recursively merge their left and right children. If one node is null, we return the non-null node.
Time Complexity: O(n); Space Complexity: O(h), where n is the total number of nodes and h is the height of the tree.
1class TreeNode {
2 int val;
3 TreeNode left;
4 TreeNode right;
5 TreeNode(int x) { val = x; }
6}
7
8public class Solution {
9 public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
10 if (t1 == null) return t2;
11 if (t2 == null) return t1;
12 t1.val += t2.val;
13 t1.left = mergeTrees(t1.left, t2.left);
14 t1.right = mergeTrees(t1.right, t2.right);
15 return t1;
16 }
17}This Java solution uses a recursive method that follows the same logic described above. It either returns the non-null node or merges the values and children recursively.
This approach uses an iterative method with a stack to simulate the recursive calls for merging the two binary trees. We traverse the trees using a stack and merge nodes at each level iteratively.
Time Complexity: O(n); Space Complexity: O(h), where n is the total number of nodes and h is the maximum height of the two trees.
1using System;
using System.Collections.Generic;
public class TreeNode {
public int val;
public TreeNode left;
public TreeNode right;
public TreeNode(int x) { val = x; }
}
public class Solution {
public TreeNode MergeTrees(TreeNode t1, TreeNode t2) {
if (t1 == null) return t2;
if (t2 == null) return t1;
Stack<TreeNode[]> stack = new Stack<TreeNode[]>();
stack.Push(new TreeNode[] { t1, t2 });
while (stack.Count > 0) {
TreeNode[] t = stack.Pop();
if (t[0] == null || t[1] == null) continue;
t[0].val += t[1].val;
if (t[0].left == null) {
t[0].left = t[1].left;
} else {
stack.Push(new TreeNode[] { t[0].left, t[1].left });
}
if (t[0].right == null) {
t[0].right = t[1].right;
} else {
stack.Push(new TreeNode[] { t[0].right, t[1].right });
}
}
return t1;
}
}This C# solution implements an iterative merging of binary trees using a Stack. As nodes are processed iteratively, their values are summed, and children are managed accordingly.