题解 | #统计农场牛数量#

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return int整型
     */
    void countNum(TreeNode* root, int & count) {
        if (root == nullptr) return;
        count += 1;
        countNum(root->left, count);
        countNum(root->right, count);
    }
    int countNodes(TreeNode* root) {
        // write code here
        int count = 0;
        countNum(root, count);
        return count;
    }
};