我根据 1 <= dist[i] <= 2 差分约束建图跑最长路。再约束 dist[1] = 0。此外，观察到原图最长路，在处理后的图上边权也应该都是 1，因此再加上限制 dist[v] = 1 (这里 v 是从 1 到 n 最长路上的点)。然而wa on test 5，期望输出No 但是我输出 Yes。

#include <bits/stdc++.h>
using namespace std;

const int N = 1e3 + 10, M = 1e5 + 10;
int e[M], nxt[M], idx = 1, h[N], hs[N], w[N];
int n, m, color[N], pre[N], dist[N];
bool st[N];
vector<pair<int, int>> edges;

void add(int a, int b) {
    e[idx] = b, nxt[idx] = h[a], h[a] = idx++;
}

void add(int a, int b, int c) {
    e[idx] = b, w[idx] = c, nxt[idx] = hs[a], hs[a] = idx++;
}

bool dfs(int u) {
    if (color[u])
        return color[u] == 2;
    color[u] = 2;
    if (pre[u] && dfs(pre[u]))
        return true;
    color[u] = 1;
    return false;
}
bool has_cycle() {
    memset(color, 0, sizeof color);
    for (int i = 1; i <= n; ++i)
        if (!color[i] && dfs(i))
            return true;
    return false;
}

bool spfa(int h[], int src) {
    queue<int> q;
    q.push(src);
    int cnt = 0;
    memset(dist, -0x3f, sizeof dist);
    dist[src] = 0;
    while (q.size()) {
        int u = q.front();
        q.pop(), st[u] = false;
        for (int i = h[u]; i; i = nxt[i]) {
            int j = e[i], d = h == hs ? w[i] : 1;
            if (dist[j] < dist[u] + d) {
                dist[j] = dist[u] + d;
                pre[j] = u;
                if (++cnt == n + 1) {
                    cnt = 0;
                    if (has_cycle())
                        return true;
                }
                if (!exchange(st[j], true))
                    q.push(j);
            }
        }
    }
    return has_cycle();
}

signed main() {
#ifndef ONLINE_JUDGE
    freopen(".in", "r", stdin);  // freopen("a.out", "w", stdout);
#else
    cin.tie(0)->sync_with_stdio(0);
#endif
    cin >> n >> m;
    while (m--) {
        int a, b;
        cin >> a >> b;
        add(a, b);
        add(b, a, -2);
        add(a, b, 1);
        edges.push_back({a, b});
    }
    spfa(h, 1);
    // for (int i = n; pre[i]; i = pre[i]) {
    //     // dist[i] - dist[pre[i]] <= 1
    //     // dist[pre[i]] >= dist[i] - 1
    //     add(i, pre[i], -1);
    // }
    // dist[n] = dist[n]
    // dist[n] >= dist[0] + dist[n]
    add(n, 1, -dist[n]), add(1, n, dist[n]);
    add(1, 0, 0), add(0, 1, 0);
    if (spfa(hs, 0))
        cout << "No";
    else {
        cout << "Yes\n";
        for (const auto& edge : edges) {
            cout << dist[edge.second] - dist[edge.first] << "\n";
        }
    }
}