力扣111. 二叉树的最小深度

/**
 * 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 minDepth(TreeNode* root) {
        if(root == nullptr) return 0;
        int left_depth = minDepth(root->left);
        int right_depth = minDepth(root->right);
        if(left_depth == 0) return right_depth + 1;
        else if(right_depth == 0) return left_depth + 1;
        
        return 1 + min(left_depth, right_depth);
    }
};