1126. Merge Two Binary Trees

最新推荐文章于 2022-03-21 16:50:58 发布

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最新推荐文章于 2022-03-21 16:50:58 发布

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博客介绍了合并两个二叉树的问题。当两个二叉树覆盖时，部分节点重叠，部分不重叠。合并规则为：重叠节点值相加作为新节点值，非空节点直接作为新树节点，并给出了输入的两个二叉树示例及合并后的输出结果。

Given two binary trees and imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while the others are not.

You need to merge them into a new binary tree. The merge rule is that if two nodes overlap, then sum node values up as the new value of the merged node. Otherwise, the NOT null node will be used as the node of new tree.

Input:
Tree 1 Tree 2
1 2
/ \ / \
3 2 1 3
/ \ \
5 4 7
Output:
Merged tree:
3
/ \
4 5
/ \ \
5 4 7

public class Solution {
    /**
     * @param t1: the root of the first tree
     * @param t2: the root of the second tree
     * @return: the new binary tree after merge
     */
    public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
        // Write your code here
        if (t1 == null && t2 == null) {
            return null;
        }

        if (t1 == null && t2 != null) {
            return t2;
        }

        if (t1 != null && t2 == null) {
            return t1;
        }

        TreeNode left = mergeTrees(t1.left, t2.left);
        TreeNode right = mergeTrees(t1.right, t2.right);

        TreeNode node = new TreeNode(t1.val + t2.val);
        node.left = left;
        node.right = right;

        return node;
    }
}