[数据结构与算法]二叉树深度搜索-前中后三序遍历

二叉树深度搜索-前中后三序遍历-递归法

分析：注意递归的三个要素

#include "_myPrint.cpp"
#include "_TreeNode.cpp"
using namespace std;

// 递归的三要素
// 参数和返回值，每层递归需要实现的逻辑，递归终止的条件
class Solution{
public:
    void travel(TreeNode* cur, vector<int>& vec){
        if (cur == NULL) return;
        vec.push_back(cur -> val);
        travel(cur -> left, vec);
        travel(cur -> right, vec);
    }
    vector<int> preorder(TreeNode* root){
        vector<int> res;
        travel(root, res);
        return res;
    }
};

int main(){
    Solution s;
    TreeNode* root = new TreeNode(8);
    TreeNode* l = new TreeNode(7);
    TreeNode* r = new TreeNode(6);

    root->left = l;
    root->right = r;
    vector<int> res = s.preorder(root);
    printCollection p;
    p.printVector(res);

}

//_TreeNode.cpp
struct TreeNode{
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};