剑指offer 给定二叉树前序，中序遍历序列，求二叉树和后续序列

#include <iostream>
#include <vector>

using namespace std;



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

class Solution {
public:
    int find_index(const vector<int>& vec, const int target){
        for(int i = 0; i < vec.size(); i++){
            if(vec[i] == target){
                return i;
            }
        }
        return -1;
    }

    TreeNode* construct(vector<int>& pre, int ps, int pe, vector<int>& vin, int vs, int ve){
        if(ps > pe) return nullptr;
        int value = pre[ps];
        int index = find_index(vin, value);
        auto node = new TreeNode(value);
        node->left = construct(pre, ps+1, ps + index - vs, vin, vs, index-1);
        node->right = construct(pre, ps + index - vs + 1, pe, vin, index + 1, ve);
        return node;
    }

    TreeNode* reConstructBinaryTree(vector<int> pre, vector<int> vin) {
        if(pre.empty() || vin.empty() || pre.size() != vin.size()){
            return nullptr;
        }
        return construct(pre, 0, pre.size()-1, vin, 0, vin.size()-1);
    }
};

void post_order(TreeNode* root){
    if(root == nullptr){
        return;
    }
    post_order(root->left);
    post_order(root->right);
    cout << root->val << ", ";
}


int main() {
    Solution s;
    vector<int> pre = {1,2,4,7,3,5,6,8};
    vector<int> vin = {4,7,2,1,5,3,8,6};
    auto t = s.reConstructBinaryTree(pre, vin);
    post_order(t);

    return 0;
}