前順遍歴と中順遍歴から後順遍歴(C+)を求める

題意は大体文字列の形式で前序遍歴と中序遍歴を入力し、後序遍歴を出力する.一つ栗↓入力:ABDEC DBEAC出力:DEBCA

#include 
#include 
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];
    //                 
    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;
}