递归
- 前序遍历
- 返回条件:树为空,返回false;路径和为sum,返回true
if (root == NULL) return false;
if (root->val == sum && root->left == NULL && root->right == NULL) return true;
- 返回:是否有满足条件的路径
return hasPathSum(root->left, sum - root->val) || hasPathSum(root->right, sum - root->val);