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;
	}
};