題目
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
方法
采用遞歸的方法。假設有2個根節(jié)點t1,t2，用t1保存最后的合并結果公黑。如果t1和t2都不為空涩维，則t1.val = t1.val+t2.val，遞歸調(diào)用賦值t1.left = mergeTrees(t1.left, t2.left)和t1.right = mergeTrees(t1.right, t2.right); 如果t1為空翔冀，t2不為空导街，則t1 = t2，最后返回t1節(jié)點
難度
Easy
python代碼
# Definition for a binary tree node.
class TreeNode(object):
def __init__(self, x):
self.val = x
self.left = None
self.right = None
class Solution(object):
def mergeTrees(self, t1, t2):
"""
:type t1: TreeNode
:type t2: TreeNode
:rtype: TreeNode
"""
if t1 and t2:
t1.val += t2.val
t1.left = self.mergeTrees(t1.left, t2.left)
t1.right = self.mergeTrees(t1.right, t2.right)
elif t2:
t1 = t2
return t1
root1 = TreeNode(1)
left1 = TreeNode(3)
right1 = TreeNode(2)
root1.left = left1
root1.right = right1
root2 = TreeNode(2)
left2 = TreeNode(1)
right2 = TreeNode(3)
root2.left = left2
root2.right = right2
root = Solution().mergeTrees(root1, root2)
assert root.val == 3
assert root.left.val == 4
assert root.right.val == 5
