617. Merge Two Binary Trees

617. Merge Two Binary Trees

DescriptionHintsSubmissionsSolutions

• Total Accepted: 5554
• Total Submissions: 7673
• Difficulty: Easy
• Contributors:jiatang

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.

Example 1:

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

Note: The merging process must start from the root nodes of both trees.

题意：

合并两个二叉树，同一个节点的值相加，如果节点都没有为空

算法思路：

用到递归的方法，用二叉树前序遍历的方法，依次求出值，最后返回根节点。

代码：

package easy;public class MergeTwoBinaryTrees { public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {        if(t1==null && t2==null){                return null;        }        if(t1==null && t2!=null){                return t2;        }        if(t1!=null && t2==null){                return t1;        }        if(t1!=null && t2!=null){        t1.val += t2.val;        t1.left = mergeTrees(t1.left, t2.left);        t1.right = mergeTrees(t1.right, t2.right);        }                return t1;    }public class TreeNode{int val;TreeNode left;TreeNode right;TreeNode(int x){val = x;}}}