【leetcode】左叶子之和

void SumLeftNode(struct TreeNode* root,int* sum,int flag)
{
    if (!root) return;
    if (flag && !root->left && !root->right) *sum += root->val;
    SumLeftNode(root->left,sum,1);
    SumLeftNode(root->right,sum,0);
}
int sumOfLeftLeaves(struct TreeNode* root){
    int sum = 0;
    SumLeftNode(root,&sum,0);
    return sum;
}