1 files changed, 68 insertions, 0 deletions
diff --git a/contests/Round#835/D/main.cpp b/contests/Round#835/D/main.cpp
new file mode 100644
index 0000000..cd81147
--- /dev/null
+++ b/contests/Round#835/D/main.cpp
@@ -0,0 +1,68 @@
+#include <algorithm>
+#include <bits/stdc++.h>
+#include <tuple>
+
+using namespace std;
+
+using ll = long long;
+using pi = pair<int, int>;
+using vpi = vector<pi>;
+using vi = vector<int>;
+using vll = vector<long long>;
+using mpii = map<int, int>;
+using mpll = map<ll, ll>;
+using db = long double;
+
+#define pb push_back
+#define all(x) (x).begin(), (x).end()
+#define rall(x) (x).rbegin(), (x).rend()
+#define lb lower_bound
+#define ub upper_bound
+
+const int MOD = (int)1e9 + 7;
+const db PI = acos((db)-1);
+const int dx[4]{1, 0, -1, 0};
+const int dy[4]{0, 1, 0, -1};
+
+int countVallyes(vi &v) {
+  int cnt = 0;
+  for (int i = 1; i < v.size() - 1; i++) {
+    if (v[i] < v[i - 1] && v[i] < v[i + 1]) {
+      cnt++;
+    }
+  }
+  return cnt;
+}
+
+void solve() {
+  int n;
+  cin >> n;
+  vi v(n + 2);
+  v[0] = INT_MAX;
+  v[n + 1] = INT_MAX;
+  for (int i = 1; i < n + 1; i++) {
+    cin >> v[i];
+  }
+  auto it = unique(all(v));
+  vi a = vector<int>(v.begin(), it);
+  cout << (countVallyes(a) == 1 ? "YES" : "NO") << '\n';
+}
+
+int main() {
+  ios_base::sync_with_stdio(false);
+  cin.tie(NULL);
+  int tt;
+  cin >> tt;
+  while (tt--) {
+    solve();
+  }
+}
+
+/* stuff you should look for:
+  ---------------------------
+   * special cases (n=1?)
+   * int overflow, array bounds
+   * do smth instead of nothing and stay organized
+   * WRITE STUFF DOWN
+   * DON'T GET STUCK ON ONE APPROACH
+ */