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package LeetCode;

/**

* 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.

* @author Administrator

*

*/

public class MergeTrees {

public MergeTrees() {

// TODO Auto-generated constructor stub

}

class TreeNode {

int val;

TreeNode left;

TreeNode right;

public TreeNode(int val) {

this.val = val;

}

}

public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {

if (t1 == null && t2 == null) return null;

if (t1 == null || t2 == null) {

return t1 == null ? t2 : t1;

}

TreeNode newRoot = recursion(t1, t2);

return newRoot;

}

private TreeNode recursion(TreeNode n1, TreeNode n2) {

if (n1 == null && n2 == null)

return null;

if (n1 == null || n2 == null) {

return n1 == null ? n2 : n1;

}

TreeNode current = new TreeNode(n1.val + n2.val);

current.left = recursion(n1.left, n2.left);

current.right = recursion(n1.right, n2.right);

return current;

}

}