POJ 3680 Intervals

题目大意

  有(n)个区间（(1 leq n leq 200))，第(i)个区间覆盖((a_{i}, b_{i}))且有权值(w_{i})（(1 leq a_{i} < b_{i} leq 100000)，(1 leq w_{i} leq 100000)），每个点最多能被覆盖(k)次（(1 leq k leq n)），求最大的权值和为多少。
 

题解

  这里点的坐标很大，所以我们要先离散化，顺便把每个点按照坐标排序。
  排完序后，我们可以从(a_{i})向(b_{i})连一条有向边，容量为(1)，费用为(w_{i})。
  同时，对于每个点(i)（(0 leq i leq cnt)，其中(cnt)表示离散化后的点数，点(0)为源点(s)，点(cnt + 1)为汇点(t)），我们要从点(i)向点(i + 1)连一条有向边，容量为(k)，费用为(0)。
  建完图后，直接跑最大费用流即可。具体细节可以参考下面的代码。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#include <algorithm>

#define MAX_N (209 + 5)

#define INF 0x3f3f3f3f

using namespace std;

struct Edge
{
    int to;
    int weight;
    int cost;
    int next;
};

int T;
int n, k;
int s, t;
int hash[100005], cnt;
int h[MAX_N << 1], tot;
Edge e[MAX_N << 3];
int dis[MAX_N << 1];
int cur[MAX_N << 1];
bool inque[MAX_N << 1], vis[MAX_N << 1];
queue <int> q;
int maxflow, mincost;

inline void AddEdge(int u, int v, int w, int c)
{
    e[++tot].to = v;
    e[tot].weight = w;
    e[tot].cost = c;
    e[tot].next = h[u];
    h[u] = tot;
    return;
}

bool SPFA()
{
    memset(dis, 0x3f, sizeof dis);
    memset(inque, 0, sizeof inque);
    memcpy(cur, h, sizeof cur);
    q.push(s);
    dis[s] = 0;
    inque[s] = true;
    int u, v, w, c;
    while(!q.empty())
    {
        u = q.front();
        q.pop();
        inque[u] = false;
        for(int i = h[u]; i; i = e[i].next)
        {
            v = e[i].to;
            w = e[i].weight;
            c = e[i].cost;
            if(dis[v] > dis[u] + c && w)
            {
                dis[v] = dis[u] + c;
                if(!inque[v])
                {
                    inque[v] = true;
                    q.push(v);
                }
            }
        }
    }
    return dis[t] != INF;
}

int DFS(int u, int flow)
{
    vis[u] = true;
    if(u == t)
    {
        maxflow += flow;
        mincost += flow * dis[t];
        return flow;
    }
    int v, w, c;
    int tmp, sum = 0;
    for(int i = cur[u]; i && sum < flow; i = e[i].next)
    {
        cur[u] = i;
        v = e[i].to;
        w = e[i].weight;
        c = e[i].cost;
        if(!vis[v] && dis[v] == dis[u] + c && w)
        {
            tmp = DFS(v, min(flow - sum, w));
            e[i].weight -= tmp;
            e[i ^ 1].weight += tmp;
            sum += tmp;
        }
    }
    return sum;
}

void Dinic()
{
    while(SPFA())
    {
        do
        {
            memset(vis, 0, sizeof vis);
            DFS(s, k);
        }
        while(vis[t]);
    }
    return;
}

int main()
{
    scanf("%d", &T);
    while(T--)
    {
        memset(h, 0, sizeof h);
        memset(e, 0, sizeof e);
        memset(hash, 0, sizeof hash);
        cnt = 0;
        tot = 1;
        maxflow = mincost = 0;
        scanf("%d%d", &n, &k);
        int u[MAX_N], v[MAX_N], c[MAX_N];
        int a[MAX_N << 1];
        for(int i = 1; i <= n; ++i)
        {
            scanf("%d%d%d", &u[i], &v[i], &c[i]);
            a[i] = u[i];
            a[i + n] = v[i];
        }
        sort(a + 1, a + n + n + 1);
        for(int i = 1; i <= n + n; ++i)
        {
            if(a[i] != a[i - 1]) hash[a[i]] = ++cnt;
        }
        for(int i = 1; i <= n; ++i)
        {
            u[i] = hash[u[i]];
            v[i] = hash[v[i]];
            AddEdge(u[i], v[i], 1, -c[i]);
            AddEdge(v[i], u[i], 0, c[i]); 
        }
        for(int i = 1; i < cnt; ++i)
        {
            AddEdge(i, i + 1, k, 0);
            AddEdge(i + 1, i, 0, 0);
        }
        s = 0;
        t = cnt + 1;
        AddEdge(s, 1, k, 0);
        AddEdge(1, s, 0, 0);
        AddEdge(cnt, t, k, 0);
        AddEdge(t, cnt, 0, k);
        Dinic();
        printf("%d
", -mincost);
    }
    return 0;
}