P1525 [NOIP2010 提高组] 关押罪犯

https://www.luogu.com.cn/record/82475050

Luogu/P1525/P1525.cpp

@@ -0,0 +1,75 @@
+#include <iostream>
+#include <array>
+#include <utility>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 20005;
+
+int n, m;
+std::array<int, N> color;
+std::array<std::vector<std::pair<int, int>>, N> g;
+
+bool dfs(int u, int color, int limit) {
+    ::color[u] = color;
+
+    for (auto e : g[u]) {
+        int v = e.first,
+            w = e.second;
+
+        if (w <= limit) continue;
+        if (::color[v]) {
+            if (::color[v] == color) return false;
+        } else if (!dfs(v, 3 - color, limit)) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+bool check(int limit) {
+    std::fill(color.begin(), color.end(), 0);
+
+    for (int i = 1; i <= n; i++) {
+        if (!color[i]) {
+            if (!dfs(i, 1, limit)) return false;
+        }
+    }
+
+    return true;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m;
+
+    for (int i = 1, u, v, w; i <= m; i++) {
+        cin >> u >> v >> w;
+
+        g[u].emplace_back(v, w);
+        g[v].emplace_back(u, w);
+    }
+
+    int l = 0, r = 1e9, ans = 0;
+
+    while (l <= r) {
+        int mid = (l + r) >> 1;
+
+        if (check(mid)) {
+            ans = mid;
+            r = mid - 1;
+        } else {
+            l = mid + 1;
+        }
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}