L2-004 这是二叉搜索树吗？

#include <bits/stdc++.h>

using namespace std;

int main() {
    int n;
    cin >> n;
    vector<int> v(n);
    for (int i = 0; i < n; i++) {
        cin >> v[i];
    }

    vector<int> res;
    function<void(int, int)> build1 = [&](int l, int r) {
        if (l > r) return;           
        int tl = l + 1, tr = r;
        while (tl <= r && v[tl] < v[l]) tl++;
        while (tr > l && v[tr] >= v[l]) tr--;
        if (tl - tr != 1) return;
        build1(l + 1, tr); 
        build1(tl, r);
        res.push_back(v[l]);
    };
    function<void(int, int)> build2 = [&](int l, int r) {
        if (l > r) return;           
        int tl = l + 1, tr = r;
        while (tl <= r && v[tl] >= v[l]) tl++;
		while (tr > l && v[tr] < v[l]) tr--;
        if (tl - tr != 1) return;
        build2(l + 1, tr); 
        build2(tl, r);
        res.push_back(v[l]);
    };

    build1(0, n - 1);
    if (res.size() == n) {
        cout << "YES" << "\n";
        for (int i = 0; i < res.size(); i++) {
            cout << res[i] << " "[i == res.size() - 1];
        } 
        return 0;
    } 

    res.clear();
    build2(0, n - 1);
    if (res.size() == n) {
        cout << "YES" << "\n";
        for (int i = 0; i < res.size(); i++) {
            cout << res[i] << " "[i == res.size() - 1];
        } 
        return 0;
    }
    cout << "NO" << "\n"; 

    return 0;
}