1760D: Challenging Valleys ⧉

If the curve has more than two local minima, then it must also have a local maximum, and hence it contains a peak. Valleys only, around here.

#if NOT_LINUX
#include "macos_includes.h"
#else
#include <bits/stdc++.h>
#endif
#if LOCAL
#include "debug.h"
#include "gxlib.h"
#else
#define dbg(...) 'x'
#endif
using namespace std;
using ll = long long;
const char nl = '\n';
const int MAX_INT = std::numeric_limits<int>::max();
const ll MAX_LL = std::numeric_limits<ll>::max();
void solve() {
  int n;
  cin >> n;
  vector<ll> a(n), adjR(n), adjL(n);
  for (auto& i : a) {
    cin >> i;
  }
  a.erase(unique(a.begin(), a.end()), a.end());
  int minima = 0;
  int m = a.size();
  for (int i = 0; i < m; ++i) {
    if (i == 0) {
      if (a[i] < a[i+1])
        minima++;
      continue;
    } else if (i == m-1) {
      if (a[i] < a[i-1])
        minima++;
      continue;
    }
    if (a[i-1] > a[i] && a[i] < a[i+1])
      minima++;
    if (minima >= 2) break;
  }
  if (minima < 2) {
    cout << "YES\n";
  } else {
    cout << "NO\n";
  }
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int t;
  cin >> t;
  for (int tc = 1; tc <= t; ++tc) {
    //cout << "Case " << tc << ":\n";
    solve();
  }
  return 0;
}

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