【LeetCode】437. Path sum III

0. summary

• The prefix and can also be used in the tree ！ Refresh your knowledge again ！
• Blog source ： [email protected]
• Source code to be updated

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1. subject

2. thought

• step1. The path from the parent node to the child node is calculated by traversing in sequence , And write the path and to the dictionary pre_sum in
• step2. In the process of traversal , Find out if there are any cur_sum - targe As pre_sum Key . If there is , It shows that there is a way to meet the conditions ,cnt+=1.
• step3. After traversing all the nodes , And you get the result res.

3. Code