The problem from Codeforces Round 925 (Div. 3)

https://codeforces.com/problemset/problem/1931/F

Signed-off-by: Frederick Chen <seventeen@ohdragonboi.cn>

codeforces/solo-problems/1931F_Chat_Screenshots.cpp

@@ -0,0 +1,51 @@
+#include <iostream>
+using namespace std;
+
+const int N = 200005;
+struct Edge{
+    int to, nxt;
+}g[N];
+int h[N], d[N], idx;
+int a[N], q[N];
+void add(int a,int b)
+{
+    g[++idx].to = b, g[idx].nxt = h[a], h[a] = idx;
+    d[b] ++;
+}
+int main()
+{
+    int n, k;
+    scanf("%d%d", &n, &k);
+    for (int i = 1; i <= n; i ++ )
+        h[i] = d[i] = 0;
+    idx = 0;
+    for (int i = 1;i <= k; i ++ )
+    {
+        for (int j = 1; j <= n; j ++ )
+            scanf("%d", &a[j]);
+        for (int j = 2; j < n; j ++ )
+            add(a[j], a[j + 1]);
+    }
+    int hh = 0, tt = -1;
+    for (int i = 1; i <= n; i ++ )
+        if (d[i] == 0)
+            q[ ++ tt] = i;
+    while (hh <= tt)
+    {
+        int t = q[hh ++];
+        for (int i = h[t]; i; i = g[i].nxt)
+        {
+            int j = g[i].to;
+            if ( -- d[j] == 0)
+                q[ ++ tt] = j;
+        }
+    }
+    for (int i = 1; i <= n; i ++ )
+        if (d[i] > 0)
+        {
+            cout << "NO";
+            return 0;
+        }
+    cout << "YES";
+    return 0;
+}