LeetCode 344 Merge Two Binary Trees

合併兩顆二叉樹, 合併規則是相同位置的值進行相加, 返回生成後二叉樹的根節點.

例 :

輸入: 
Tree 1Tree 2
12
/ \/ \
3213
/\\
547
輸出: 
3
/ \
45
/ \\ 
 547

解法

基本思路是將兩棵樹, 合併到左樹上, 基本規則是隻有當tree1 和tree2 相同位置的節點都不為空時, 才能進行相加操作, 當tree1 為空時, 把tree2 的節點嫁接 過來, 當tree2 為空時, 保留tree1 即可. 以此類推, 把每個節點都看成根節點即可.

class Solution {
public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
if (t1 == null) {
return t2;
} else if (t2 == null) {
return t1;
}

t1.val += t2.val;
t1.left = mergeTrees(t1.left, t2.left);
t1.right = mergeTrees(t1.right, t2.right);
return t1;
}
}

Runtime: 0 ms, faster than 100.00% of Java online submissions for Merge Two Binary Trees. Memory Usage: 41.2 MB, less than 78.32% of Java online submissions for Merge Two Binary Trees.