输入后序+中序，输出前序。

考试时候代码

#include <iostream>
#include <vector>
using namespace std;
const int N = 100;
vector<int> resVector;
int arr1[N], arr2[N], res[N];
struct TreeNode {
   int val;
   TreeNode *left;
   TreeNode *right;
   TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
TreeNode* getTree(int* a1, int left1, int right1, int* a2, int left2, int right2) {
  if (left1>right1) return NULL;
  if (left1==right1) return new TreeNode(a1[left1]);

  int rootVal = a1[right1]; // 后序遍历，根
  int splitIndex = right2;
  while(a2[splitIndex] != rootVal) splitIndex--;
  TreeNode* tempRes = new TreeNode(rootVal); //
  tempRes->left = getTree(a1, left1, left1+(splitIndex-1-left2), a2, left2, splitIndex-1);
  tempRes->right = getTree(a1, left1+(splitIndex-1-left2)+1, right1-1, a2, splitIndex+1, right2);
  return tempRes;
}
void preOrder(TreeNode * node) {
  if(!node) return;
  resVector.push_back(node->val);
  preOrder(node->left);
  preOrder(node->right);
}
int main () {
  int n;
  cin >> n;
  for (int i=0; i<n; i++) cin >> arr1[i];
  for (int j=0; j<n; j++) cin >> arr2[j];
  int idx = 0;
  TreeNode* resRoot = getTree(arr1, 0, n-1, arr2, 0, n-1);
  preOrder(resRoot);
  for(int i=0; i<resVector.size(); i++) {
      cout << resVector[i];
      if(i!=resVector.size()-1) cout << " ";
  }
  return 0;
}

稍稍优化了一下

#define  _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <vector>
using namespace std;
vector<int> resVector;
struct TreeNode {
  TreeNode* left;
  TreeNode* right;
  int val;
  TreeNode(int _val) : val(_val),left(NULL),right(NULL){}
};
TreeNode* getTree(vector<int>& postArr, int left1, int right1, vector<int> midArr, int left2, int right2) {
  if (left1 > right1) return NULL;
  if (left1 == right1) return new TreeNode(postArr[left1]);
  int rootVal = postArr[right1];
  int splitIndex = right2;
  while (midArr[splitIndex] != rootVal) splitIndex--;
  TreeNode* tempRes = new TreeNode(rootVal);
  tempRes->left = getTree(postArr, left1, left1+(splitIndex-1-left2), midArr, left2, splitIndex - 1);
  tempRes->right = getTree(postArr, left1 + (splitIndex - 1 - left2) + 1, right1 - 1, midArr, splitIndex + 1, right2);
  return tempRes;
}
void preOrderTrav(TreeNode* node) {
  if (node == NULL) return;
  resVector.push_back(node->val);
  preOrderTrav(node->left);
  preOrderTrav(node->right);
}
int main() {
  int n;
  cin >> n;
  vector<int> postOrderArr(n), midOrderArr(n);
  for (int i = 0; i < n; i++) cin >> postOrderArr[i];
  for (int i = 0; i < n; i++) cin >> midOrderArr[i];
  TreeNode* res = getTree(postOrderArr, 0, n - 1, midOrderArr, 0, n - 1);
  preOrderTrav(res);
  for (int i = 0; i < n; i++) {
      cout << resVector[i];
      if (i != n - 1) cout << " ";
  }
  // system("pause");
  return 0;
}