Day10 Path Sum

LeetCode112. Path Sum

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

For example:
Given the below binary tree and sum = 22,

              5
             / \
            4   8
           /   / \
          11  13  4
         /  \      \
        7    2      1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

有一个注意的地方，就是需要保存当前结点处的和，即从根节点到当前结点按照某一路径加起来的和。保存的话，把那个和赋给当前结点的val就行了。

每次只在遇到叶结点时，才检查那个和是否满足等于sum。

遍历的方法，用递归或者栈或者队列，深度优先，宽度优先都行。