113. Path Sum II刷题笔记

用迭代法可以解决这个搜索问题

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def pathSum(self, root: Optional[TreeNode], targetSum: int) -> List[List[int]]:
        if not root:
            return []
        que = deque([root])
        temp = deque([(root.val,[root.val])])
        result = []
        while que:
            for _ in range(len(que)):
                node = que.popleft()
                value, path = temp.popleft()
                if not node.left and not node.right:
                    if value == targetSum:
                        result.append(path)
                else:
                    if node.left:
                        que.append(node.left)
                        temp.append((node.left.val+value,path+[node.left.val]))
                    if node.right:
                        que.append(node.right)
                        temp.append((node.right.val+value,path+[node.right.val]))
        return result