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81 lines
2.5 KiB
C++
81 lines
2.5 KiB
C++
#define _CRT_SECURE_NO_WARNINGS
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#define _SILENCE_CXX17_C_HEADER_DEPRECATION_WARNING
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#include <bits/stdc++.h>
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using namespace std;
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const int N = 2050, inf = 0x3f3f3f3f;
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int adj[N], nxt[N << 1], to[N << 1], cap[N << 1], cur[N], cnt[N], dis[N], fa[N], ecnt;
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inline void addEdge_impl_(int f, int t, int c)
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{
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nxt[ecnt] = adj[f];
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adj[f] = ecnt;
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to[ecnt] = t;
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cap[ecnt] = c;
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ecnt++;
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}
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inline void addEdge(int f, int t, int c)
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{
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addEdge_impl_(f, t, c);
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addEdge_impl_(t, f, 0);
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}
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int ISAP(int S, int T)
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{
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int flow = 0;
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for (int &di : dis) di = N - 1;
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int len = 0, x;
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static int que[N];
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dis[que[len++] = T] = 0;
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for (int i = 0; i < len; i++)
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for (int e = adj[x = que[i]]; ~e; e = nxt[e])
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if (cap[e ^ 1] && dis[to[e]] > dis[x] + 1)
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dis[que[len++] = to[e]] = dis[x] + 1;
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memset(cnt, 0, sizeof(cnt));
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for (int i = 0; i < N; i++) cur[i] = adj[i], cnt[dis[i]]++;
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x = S;
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while (dis[S] < N - 1)
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{
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if (x == T)
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{
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int curFlow = inf;
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for (x = T; x != S; x = to[fa[x] ^ 1]) curFlow = min(curFlow, cap[fa[x]]);
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for (x = T; x != S; x = to[fa[x] ^ 1]) cap[fa[x]] -= curFlow, cap[fa[x] ^ 1] += curFlow;
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flow += curFlow, x = S;
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}
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bool needRetreat = true;
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for (int e = cur[x]; needRetreat && ~e; e = nxt[e])
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if (cur[x] = e, cap[e] && dis[x] == dis[to[e]] + 1)
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needRetreat = false, fa[x = to[e]] = e;
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if (needRetreat)
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{
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int nd = N - 2;
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for (int e = adj[x]; ~e; e = nxt[e])
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if (cap[e]) nd = min(nd, dis[to[e]]);
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if (--cnt[dis[x]] == 0) break;
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++cnt[dis[x] = nd + 1];
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cur[x] = adj[x];
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if (x != S) x = to[fa[x] ^ 1];
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}
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}
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return flow;
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}
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int main()
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{
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memset(adj, -1, sizeof(adj)), ecnt = 0;
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int n, m;
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scanf("%d%d", &m, &n);
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for (int i, j; scanf("%d%d", &i, &j), ~(i & j);)
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addEdge(i, j, 1);
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for (int i = 1; i <= m; i++) addEdge(0, i, 1);
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for (int j = m + 1; j <= n; j++) addEdge(j, n + 1, 1);
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int flow = ISAP(0, n + 1);
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if (flow)
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{
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printf("%d\n", flow);
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for (int f = 1; f <= m; f++)
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for (int e = adj[f]; ~e; e = nxt[e])
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if (cap[e ^ 1] && m < to[e] && to[e] <= n)
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printf("%d %d\n", f, to[e]);
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}
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else
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puts("No Solution!");
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return 0;
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} |