136SumofLeftLeaves.cpp

#include <iostream>
using namespace std;

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;

    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
};

class Solution {
public:
    int sumOfLeftLeaves(TreeNode* root) {
        if (root == nullptr) return 0;

        int sum = 0;

        if (root->left && root->left->left == nullptr && root->left->right == nullptr) {
            sum += root->left->val;
        }

        sum += sumOfLeftLeaves(root->left);
        sum += sumOfLeftLeaves(root->right);

        return sum;
    }
};

int main() {
    /*
            3
           / \
          9   20
             /  \
            15   7
    */

    TreeNode* root = new TreeNode(3);
    root->left = new TreeNode(9);
    root->right = new TreeNode(20);
    root->right->left = new TreeNode(15);
    root->right->right = new TreeNode(7);

    Solution obj;
    cout << obj.sumOfLeftLeaves(root) << endl; // 24

    return 0;
}