根据前序遍历与中序遍历 求出后序遍历（C++）

题意大概是以字符串的形式输入前序遍历和中序遍历，输出后序遍历。
一个栗子 ↓
输入：ABDEC DBEAC
输出：DEBCA

#include <iostream>
#include <string.h>
using namespace std;

void findPostorder(string preorder, int low_1, int high_1, string inorder, int low_2, int high_2, char* postorder, int low_3, int high_3) {   
    if (low_1 == high_1) {
        postorder[high_3] = preorder[low_1];
        return; 
    }
    int i;
    for (i = low_2; i <= high_2; i++) {
        if (preorder[low_1] == inorder[i]) {
            break;
        }
    }
    postorder[high_3] = preorder[low_1]; 
    findPostorder(preorder, low_1 + 1, low_1 + i, inorder, low_2, low_2 + i - 1, postorder, low_3, low_3 + i - 1);
    findPostorder(preorder, low_1 + i + 1, high_1, inorder, low_2 + i + 1, high_2, postorder, low_3 + i, high_3 - 1);
}

int main() {
    string preorder, inorder;
    cin >> preorder >> inorder;
    int length = preorder.size();
    char postorder[length];
    //对后序遍历所在的字符串数组进行填充
    findPostorder(preorder, 0, length - 1, inorder, 0, length - 1, postorder, 0, length - 1);
    for (int i = 0; i < length; i++) {
        cout << postorder[i];
    }
    return 0;
}