模板笔记

欧拉回路

\(\color{CornflowerBlue}{【uoj\ 117】}\)

#include <cstdio>

const int N = 100005, M = 200005;
int head[N], nxt[M<<1], pnt[M<<1], tot = 1, in[N], out[N], vis[M], ans[M], cnt;

int read() {
    int x = 0; char c = getchar();
    while (c < '0' || c > '9') c = getchar();
    while (c >= '0' && c <= '9') {
        x = (x << 3) + (x << 1) + (c ^ 48);
        c = getchar();
    }
    return x;
}
void add_edge(int u, int v) {
    nxt[++tot] = head[u];
    head[u] = tot, pnt[tot] = v;
}
void dfs(int cur) {
    for (int &i = head[cur], j; i; i = nxt[i]) {
        if (vis[(j=i)>>1]) continue;
        vis[j>>1] = 1, dfs(pnt[j]), ans[++cnt] = j;
    }
}

int main() {
    int t = read(), n = read(), m = read();
    for (int i = 1; i <= m; ++i) {
        int u = read(), v = read();
        add_edge(u, v);
        if (t == 2) ++out[u], ++in[v], ++tot;
        else add_edge(v, u), ++in[u], ++in[v];
    }
    if (t == 1) {
        for (int i = 1; i <= n; ++i)
            if (in[i] & 1) { puts("NO"); return 0; }
    } else {
        for (int i = 1; i <= n; ++i)
            if (in[i] != out[i]) { puts("NO"); return 0; }
    }
    dfs(pnt[2]);
    if (cnt < m) puts("NO");
    else {
        puts("YES");
        for (int i = cnt; i; --i)
            printf("%d ", (ans[i] >> 1) * (ans[i] & 1 ? -1 : 1));
    }
    return 0;
}