LeetCode[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.

加一个parent参数，来判断当前叶子节点node是否为某节点的左孩子

/**
* 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 == NULL)
return 0;
return sumOfLeftLeaves(root, NULL);
}
int sumOfLeftLeaves(TreeNode* node, TreeNode* parent) {
int sum = 0;
if (node->left)
sum += sumOfLeftLeaves(node->left, node);
if (node->right)
sum += sumOfLeftLeaves(node->right, node);
if (node->left == NULL && node->right == NULL && parent != NULL && parent->left == node)
sum += node->val;
return sum;
}
};