信息学竞赛入门了

#include <iostream>
#include <vector>
#include <tuple>

using namespace std;
int n, x, w, l, r;

struct TreeNode {
  int val;
  TreeNode* left;
  TreeNode* right;
  TreeNode() : val(0), left(nullptr), right(nullptr) {};
  TreeNode(int _val) : val(_val), left(nullptr), right(nullptr) {};
  TreeNode(int _val, TreeNode* _left, TreeNode* _right) : val(_val), left(nullptr), right(nullptr) {};
  ~TreeNode() {}
};

TreeNode* buildTree(vector<tuple<int, int, int>>& data, int idx) {
  // recursion exit condition (base case)
  if (!idx) return nullptr;

  const int w = get<0>(data[idx]);
  const int l = get<1>(data[idx]);
  const int r = get<2>(data[idx]);

  auto root   = new TreeNode(w);
  root->left  = buildTree(data, l);
  root->right = buildTree(data, r);
  return root;
}

void inOrder(TreeNode* root, vector<int>& vals) {
  if (!root) return;
  inOrder(root->left,  vals);
  vals.emplace_back(root->val);
  inOrder(root->right, vals);
}

int main(void) {
  scanf("%d %d", &n, &x);
  // tuple(weight, left, right) 三元组
  vector<tuple<int, int, int>> data(n + 1);
  for (int i = 1; i <= n; ++i) {
    scanf("%d %d %d", &w, &l, &r);
    data[i] = {w, l, r };
  }

  vector<int> vals;
  auto root = buildTree(data, 1);
  inOrder(root, vals);

  int ans = 0;
  for (int i = 0; i < vals.size(); ++i)
    if (vals[i] == x) { ans = i + 1; break; }

  printf("%d\n", ans);
}