Leetcode 617. 合并二叉树

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Leetcode 617. 合并二叉树

题目：

给定两个二叉树，想象当你将它们中的一个覆盖到另一个上时，两个二叉树的一些节点便会重叠。

你需要将他们合并为一个新的二叉树。合并的规则是如果两个节点重叠，那么将他们的值相加作为节点合并后的新值，否则不为 NULL 的节点将直接作为新二叉树的节点。

输入: 
	Tree 1                     Tree 2                  
          1                         2                             
         / \                       / \                            
        3   2                     1   3                        
       /                           \   \                      
      5                             4   7                  
输出: 
合并后的树:
	     3
	    / \
	   4   5
	  / \   \ 
	 5   4   7

题解：

 public static TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
        if (t1 == null) {
            return t2;
        }
        if (t2 == null) {
            return t1;
        }

        TreeNode treeNode = new TreeNode(t1.value + t2.value);
        Queue<TreeNode> queue = new LinkedList<>();
        Queue<TreeNode> queue1 = new LinkedList<>();
        Queue<TreeNode> queue2 = new LinkedList<>();

        queue.add(treeNode);
        queue1.add(t1);
        queue2.add(t2);

        while (!queue1.isEmpty() && !queue2.isEmpty()) {
            TreeNode node = queue.poll();
            TreeNode treeNode1 = queue1.poll();
            TreeNode treeNode2 = queue2.poll();

            TreeNode left1 = treeNode1.left;
            TreeNode right1 = treeNode1.right;
            TreeNode left2 = treeNode2.left;
            TreeNode right2 = treeNode2.right;

            if (left1 != null || left2 != null) {
                if (left1 != null && left2 != null) {
                    TreeNode left = new TreeNode(left1.value + left2.value);
                    node.left = left;
                    queue.add(left);
                    queue1.add(left1);
                    queue2.add(left2);
                } else if (left1 != null) {
                    node.left = left1;
                } else if (left2 != null) {
                    node.left = left2;
                }
            }


            if (right1 != null || right2 != null) {
                if (right1 != null && right2 != null) {
                    TreeNode right = new TreeNode(right1.value + right2.value);
                    node.right = right;
                    queue.add(right);
                    queue1.add(right1);
                    queue2.add(right2);
                } else if (right1 != null) {
                    node.right = right1;
                } else if (right2 != null) {
                    node.right = right2;
                }
            }
        }
        return treeNode;
    }

public static TreeNode mergeTrees(TreeNode t1, TreeNode t2) {

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

        Queue<TreeNode> q1 = new LinkedList<>();
        Queue<TreeNode> q2 = new LinkedList<>();

        q1.add(t1);
        q2.add(t2);

        while (!q1.isEmpty()) {
            TreeNode n1 = q1.poll();
            TreeNode n2 = q2.poll();
            if (n1.left != null && n2.left != null) {
                q1.add(n1.left);
                q2.add(n2.left);
            } else if (n1.left == null) {
                n1.left = n2.left;
            }

            if (n1.right != null && n2.right != null) {
                q1.add(n1.right);
                q2.add(n2.right);
            } else if (n1.right == null) {
                n1.right = n2.right;
            }
            n1.value = n1.value + n2.value;

        }
        return t1;
    }