【leetcode刷题】T134-左叶子之和

示例：
    3
   / \
  9  20
    /  \
   15   7
在这个二叉树中，有两个左叶子，分别是 9 和 15，所以返回 24

# 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 sumOfLeftLeaves(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root:
            return 0
        return self.get_sum(False, root)

    def get_sum(self, is_left, node):
        if not node.left and not node.right:
            if is_left:
                return node.val
            else:
                return 0
        res = 0
        if node.left:
            res += self.get_sum(True, node.left)
        if node.right:
            res += self.get_sum(False, node.right)
        return res

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int sumOfLeftLeaves(TreeNode* root) {
        if(!root)
            return 0;
        return get_sum(false, root);
    }

    int get_sum(bool is_left, TreeNode* node){
        if(!node->left && !node->right){
            if(is_left)
                return node->val;
            else
                return 0;
        }
        int res = 0;
        if(node->left)
            res += get_sum(true, node->left);
        if(node->right)
            res += get_sum(false, node->right);
        return res;
    }
};