二叉树前中后序遍历cpp

title

#include <cstdio>
#include <cstring>
#include <iostream>
using namespace std;

/*
前序 HGEDBFCA, 中序 EGBD H FAC, 后序 EBDGACFH,
 root : H
 left : EGBD
 root : FAC
*/
void reqBackOrder(string middle, string front) {
  if (middle.size() > 0) {
    char root = front[0];
    int k = middle.find(root);
    reqBackOrder(middle.substr(0, k), front.substr(1, k)); // left
    reqBackOrder(middle.substr(k + 1), front.substr(k + 1, middle.size() - k - 1));
    cout << root;
  }
}

void reqFrontOrder(string middle, string after) {
  if (middle.size() > 0) {
    char root = after[after.size() - 1];
    cout << root;
    int k = middle.find(root);
    reqFrontOrder(middle.substr(0, k), after.substr(0, k));
    reqFrontOrder(middle.substr(k + 1), after.substr(k, middle.size() - k - 1));
  }
}

int main(int argc, char *argv[]) {
  char flag;
  if (argc != 2) {
    cout << "need arg: 0 or 1 indicate front or back" << endl;
    return 0;
  }
  flag = argv[1][0];

  string middle;
  if ('0' == flag) {
    string front;
    cout << "input front order string" << endl;
    cin >> front;
    cout << "input middle order string" << endl;
    cin >> middle;

    cout << "back order string:";
    reqBackOrder(middle, front);
  } else {
    string back;
    cout << "input middle order string" << endl;
    cin >> middle;
    cout << "input middle back string" << endl;
    cin >> back;
    cout << "front order string:";
    reqFrontOrder(middle, back);
  }

  cout << endl;
  return 0;
}