Uvalive 2957 Bring Them There

来源：互联网发布：java重要的知识点总结编辑：程序博客网时间：2024/04/29 08:00
拆点网络流，方法很巧妙。
#include<algorithm>#include<iostream>#include<cstring>#include<cstdio>#include<vector>#include<queue>#include<cmath>#include<stack>#include<cmath>#include<set>#include<map>#define LL long long#define CLR(a, b) memset(a, b, sizeof(a))using namespace std;const int maxn = 2020;const int INF = 0x3f3f3f3f;struct Edge{    int from, to, cap, flow;    Edge() {}    Edge(int from, int to, int cap, int flow)        :from(from), to(to), cap(cap), flow(flow) {}};struct ISAP{    int n, m, s, t;    vector<Edge> edges;    vector<int> G[maxn];    bool vis[maxn];    int d[maxn], cur[maxn];    int p[maxn], num[maxn];    void init()    {        edges.clear();    }    void ClearEdge(int bn, int n)    {        this->n = n;        for(int i = bn; i < n; i ++) G[i].clear();    }    void ClearFlow()    {        for(int i = 0; i < edges.size(); i ++)            edges[i].flow = 0;    }    void AddEdge(int from, int to, int cap)    {        edges.push_back(Edge(from, to, cap, 0));        edges.push_back(Edge(to, from, 0, 0));        m = edges.size();        G[from].push_back(m-2);        G[to].push_back(m-1);    }    bool BFS()    {        CLR(vis, false);        queue<int> Q;        Q.push(t);        vis[t] = 1; d[t] = 0;        while(!Q.empty())        {            int x = Q.front(); Q.pop();            for(int i = 0; i < G[x].size(); i ++)            {                Edge& e = edges[G[x][i]^1];                if(!vis[e.from] && e.cap > e.flow)                {                    vis[e.from] = true;                    d[e.from] = d[x] + 1;                    Q.push(e.from);                }            }        }        return vis[s];    }    int Augment()    {        int x = t, a = INF;        while(x != s)        {            Edge& e = edges[p[x]];            a = min(a, e.cap-e.flow);            x = edges[p[x]].from;        }        x = t;        while(x != s)        {            edges[p[x]].flow += a;            edges[p[x]^1].flow -= a;            x = edges[p[x]].from;        }        return a;    }    int Maxflow(int s, int t, int limit)    {        this->s = s; this->t = t;        int flow = 0;        BFS();CLR(num, 0);        for(int i = 0; i < n; i ++) num[d[i]] ++;        int x = s;        CLR(cur, 0);        while(d[s] < n)        {            if(x == t)            {                flow += Augment();                if(flow >= limit) return flow;                x = s;            }            int ok = 0;            for(int i = cur[x]; i < G[x].size(); i ++)            {                Edge& e = edges[G[x][i]];                if(e.cap > e.flow && d[x] == d[e.to] + 1)                {                    ok = 1;                    p[e.to] = G[x][i];                    cur[x] = i;                    x = e.to;                    break;                }            }            if(!ok)            {                int m = n - 1;                for(int i = 0; i < G[x].size(); i ++)                {                    Edge& e = edges[G[x][i]];                    if(e.cap > e.flow) m = min(m, d[e.to]);                }                if(-- num[d[x]] == 0) break;                num[d[x] = m + 1] ++;                cur[x] = 0;                if(x != s) x = edges[p[x]].from;            }        }        return flow;    }    void Reduce()    {        for(int i = 0; i < edges.size(); i ++)            edges[i].cap -= edges[i].flow;    }    vector<int> Mincut()    {        vector<int> ans;        BFS();        for(int i = 0; i < edges.size(); i ++)        {            Edge e = edges[i];            if(!vis[e.from] && vis[e.to] && e.cap > 0) ans.push_back(i);        }        return ans;    }} sol;vector<pair<int, int> > path, ans;int main(){    int n, m, k, s, t;    while(scanf("%d%d%d%d%d", &n, &m, &k, &s, &t) != EOF)    {        s --; t --;        path.clear();        for(int i = 0; i < m; i ++)        {            int u, v;            scanf("%d%d", &u, &v);            path.push_back(make_pair(-- u, -- v));        }        int day = 0, maxflow = 0;        sol.init();sol.ClearEdge(0, n);        while(maxflow < k)        {            int last = day * n, now = last + n;            sol.ClearEdge(now, now + n);            for(int i = 0; i < n; i ++)                sol.AddEdge(last + i, now + i, INF);            for(int i = 0; i < m; i ++)            {                int u = path[i].first, v = path[i].second;                sol.AddEdge(last + u, now + v, 1);                sol.AddEdge(last + v, now + u, 1);            }            maxflow += sol.Maxflow(s, t + now, k - maxflow);            day ++;        }        printf("%d\n", day);        vector<int> loc(k, s);        for(int i = 0, j = 0; i < day; i ++)        {            j += 2 * n;            ans.clear();            while(j < (i + 1) * (2 * n + 4 * m))            {                bool f1 = false, f2 = false;                Edge e1 = sol.edges[j];                if(e1.flow == 1) f1 = true;                j += 2;                Edge e2 = sol.edges[j];                if(e2.flow == 1) f2 = true;                j += 2;                if(f1 && !f2) ans.push_back(make_pair(e1.from % n, e1.to % n));                if(!f1 && f2) ans.push_back(make_pair(e2.from % n, e2.to % n));            }            printf("%d", ans.size());            vector<int> mov(k, 0);            for(int i = 0; i < ans.size(); i ++)            {                int u = ans[i].first, v = ans[i].second;                for(int j = 0; j < k; j ++)                {                    if(loc[j] == u && !mov[j])                    {                        mov[j] = 1;                        loc[j] = v;                        printf(" %d %d", j + 1, v + 1);                        break;                    }                }            }puts("");        }    }}
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