leetcode-Minimum Depth of Binary Tree

class Solution {
public:
    int minDepth(TreeNode *root) {
        if (root == nullptr) return 0;
        if (root->left != nullptr&&root->right != nullptr)
        {
            int lDepth = minDepth(root->left);
            int rDepth = minDepth(root->right);
            return (lDepth<rDepth?lDepth+1:rDepth+1);
        }
        if (root->left != nullptr)
        {
            return 1+minDepth(root->left);
        }
        if (root->right != nullptr)
        {
            return 1+minDepth(root->right);
        }
        return 1;//只有一个根节点时。
    }
};