'commit'

TangDou/AcWing/EulerPath/UOJ117.cpp

@@ -0,0 +1,68 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+typedef pair<int, int> PII;
+const int N = 1e5 + 10, M = 2e5 + 10;
+vector<PII> g[N];
+int st[M];
+int ans[M], al;
+int din[N], dout[N];
+int op, n, m;
+
+// 需要删边优化
+void dfs(int u) {
+    while (g[u].size()) {
+        PII x = g[u].back();
+        g[u].pop_back();
+
+        int v = x.first, id = x.second, fid = abs(id);
+        if (st[fid]) continue;
+        st[fid] = 1;
+        dfs(v);
+        ans[++al] = id; // 记录的是边号
+    }
+}
+// 检查是不是存在欧拉回路
+bool check() {
+    int start = 1;
+    if (op == 2) {
+        for (int i = 1; i <= n; i++) {
+            if (din[i] != dout[i]) return 0;
+            if (din[i]) start = i;
+        }
+    } else {
+        for (int i = 1; i <= n; i++) {
+            if ((din[i] + dout[i]) & 1) return 0;
+            if (din[i] + dout[i]) start = i;
+        }
+    }
+    // 判连通，找出欧拉回路
+    dfs(start);
+    if (al < m) return 0;
+
+    return 1;
+}
+
+int main() {
+#ifndef ONLINE_JUDGE
+    freopen("UOJ117.in", "r", stdin);
+#endif
+
+    scanf("%d %d %d", &op, &n, &m);
+    for (int i = 1; i <= m; i++) {
+        int a, b;
+        scanf("%d%d", &a, &b);
+        g[a].push_back({b, i});               // 对边点，边号
+        if (op == 1) g[b].push_back({a, -i}); // 无向图
+        din[b]++, dout[a]++;
+    }
+
+    if (!check()) {
+        puts("NO");
+        return 0;
+    }
+
+    puts("YES");
+    for (int i = al; i; i--) printf("%d ", ans[i]);
+    return 0;
+}