左叶子之和

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int result=0;
    void left_sum(TreeNode* cur)
    {
        if(cur==nullptr) return ;
        //判断左子叶
        if(cur->left!=nullptr&&cur->left->left==nullptr&&cur->left->right==nullptr) 
        	result += cur->left->val;
        left_sum(cur->left);
        left_sum(cur->right);

    }
    int sumOfLeftLeaves(TreeNode* root) {
        left_sum(root);
        return result;
    }
};

二刷

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int result = 0;
    void find_tree(TreeNode* cur , int left_flag)
    {
        if(cur==nullptr) return;
        if(cur->left==nullptr&&cur->right==nullptr&&left_flag==1)
            result += cur->val;
        find_tree(cur->left,1);
        find_tree(cur->right,0);
        return;
    }
    int sumOfLeftLeaves(TreeNode* root) {
        if(root == nullptr) return 0;
        find_tree(root,0);
        return result;
    }
};