'commit'

TangDou/AcWing/Floyd/1471.cpp

@@ -0,0 +1,32 @@
+#include <bits/stdc++.h>
+using namespace std;
+const int N = 110;
+int n, d[N][N], ans;
+int main() {
+    scanf("%d", &n);
+
+    int u, v;
+    for (int i = 1; i < n; i++) scanf("%d%d", &u, &v), d[u][v] = 1;
+
+    // Floyd求传递闭包
+    for (int k = 1; k <= n; k++)
+        for (int i = 1; i <= n; i++)
+            for (int j = 1; j <= n; j++)
+                d[i][j] |= d[i][k] & d[k][j];
+
+    for (int i = 1; i <= n; i++) {
+        int cnt = 0;
+        for (int j = 1; j <= n; j++)
+            if (d[j][i]) cnt++; //有多少个点可以到达i点
+
+        if (cnt == n - 1) {
+            ans = i;
+            break;
+        }
+    }
+    if (ans)
+        printf("%d", ans);
+    else
+        puts("-1");
+    return 0;
+}