404. Sum of Left Leaves

Find the sum of all left leaves in a given binary tree.

Example:

    3
   / \
  9  20
    /  \
   15   7

There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

DFS:https://leetcode.com/problems/sum-of-left-leaves/discuss/88950
BFS:https://leetcode.com/problems/sum-of-left-leaves/discuss/89060

Solution：

思路：

Time Complexity: O(N) Space Complexity: O(N)

Solution Code：