E - Bichromization

https://atcoder.jp/contests/keyence2020/submissions/36537145

AtCoder/keyence2020/E/E.cpp

@@ -0,0 +1,73 @@
+#include <iostream>
+#include <algorithm>
+#include <queue>
+#include <utility>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5,
+          M = 2e5 + 5;
+
+int n, m, a[N], ans[M];
+std::vector<std::pair<int, int>> g[N];
+char c[N];
+std::queue<int> q;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+    }
+
+    for (int i = 1, u, v; i <= m; i++) {
+        cin >> u >> v;
+
+        g[u].emplace_back(v, i);
+        g[v].emplace_back(u, i);
+
+        if (a[u] == a[v] && !c[u] && !c[v]) {
+            c[u] = 'W';
+            c[v] = 'B';
+            q.emplace(u);
+            q.emplace(v);
+            ans[i] = a[u];
+        }
+    }
+
+    while (!q.empty()) {
+        int u = q.front();
+        q.pop();
+
+        for (auto e : g[u]) {
+            int v = e.first,
+                id = e.second;
+
+            if (!c[v] && a[u] <= a[v]) {
+                c[v] = c[u] == 'W' ? 'B' : 'W';
+                ans[id] = a[v];
+                q.emplace(v);
+            }
+        }
+    }
+
+    if (std::count(c + 1, c + 1 + n, '\0')) {
+        cout << -1 << endl;
+
+        exit(0);
+    }
+
+    cout << c + 1 << endl;
+
+    for (int i = 1; i <= m; i++) {
+        cout << (ans[i] ? ans[i] : 1000000000) << endl;
+    }
+
+    return 0;
+}