算法——先序中序还原二叉树

晴问算法

记得在dfs那里给指针和数组加&，指针不加不会修改，数组不加会报错

#include <bits/stdc++.h>

using namespace std;

vector<int> preOrder, inOrder;
vector<int> result;


struct TreeNode {
    int data;
    TreeNode *left;
    TreeNode *right;

    TreeNode(int data) : data(data), left(nullptr), right(nullptr) {}
};


void dfs(TreeNode* &root, vector<int> &pre, vector<int> &in) {
    if (pre.empty()||in.empty()) return;
    int rootNum = pre[0];
    root = new TreeNode(rootNum);
    int root_Index;
    for (root_Index = 0; root_Index < in.size(); ++root_Index) {
        if (in[root_Index] == rootNum) break;
    }

    vector<int> vec1(pre.begin() + 1, pre.begin() + root_Index + 1);
    vector<int> vec2(pre.begin() + root_Index + 1, pre.end());
    vector<int> vec3(in.begin(), in.begin() + root_Index);
    vector<int> vec4(in.begin() + root_Index + 1, in.end());

    dfs(root->left, vec1, vec3);
    dfs(root->right, vec2, vec4);


}


void PostOrder(TreeNode *root) {
    if (root == nullptr) return;
    PostOrder(root->left);
    PostOrder(root->right);
    result.push_back(root->data);
}

int main() {

    int n;
    cin >> n;

    for (int i = 0; i < n; ++i) {
        int num;
        cin >> num;
        preOrder.push_back(num);
    }
    for (int i = 0; i < n; ++i) {
        int num;
        cin >> num;
        inOrder.push_back(num);
    }

    TreeNode *root;
    dfs(root, preOrder, inOrder);
    PostOrder(root);

    for (int i = 0; i < result.size(); ++i) {
        if (i != 0) cout << " ";
        cout << result[i];
    }

    return 0;
}