404. Sum of Left Leaves

Solution

• We use bool variable isLeft to indicate whether the current node is left child or not.
• Rest is just sum of leaf node with isLeft = true.

Code

class Solution {
private:
    int sum = 0;

public:
    int sumOfLeftLeaves(TreeNode* root, bool isLeft = false)
    {
        if (root == NULL) return 0;
        if (isLeft && root->left == NULL && root->right == NULL) sum += root->val;
        sumOfLeftLeaves(root->left, true);
        sumOfLeftLeaves(root->right, false);
        return sum;
    }
};