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.

題目要求樹的所有左葉節點的和，根據題意判斷出所有左葉節點，使用遞歸即可。

class Solution {
public:
    int sumOfLeftLeaves(TreeNode* root) {
        
 
if (root == nullptr)
            return 0;
        if (root->left != nullptr && root->left->left == nullptr && root->left->right == nullptr)
            return root->left->val + sumOfLeftLeaves(root->right);
        return sumOfLeftLeaves(root->left) + sumOfLeftLeaves(root->right);
    }
};
 
// 6 ms

[LeetCode] Sum of Left Leaves