[二分+线段树构图+网络流]CodeForces 589FGourmet and Banquet

题目大意：给定n道菜，每道菜出现的时间ai和消失的时间bi。每个单位时间内只能品尝一道菜，要保证每道菜所品尝的次数相同。求最多能吃多少道菜。

题解：二分答案+线段树构图+网络流
（据说有贪心做法，为什么大家都那么神呢？=_=）

代码：

#include <cstdio>#include <cstdlib>#include <cstring>#include <algorithm>#include <iostream>#include <queue>using namespace std;int n,maxx;int head[161000],nextt[2010000],ver[2010000],edge[2010000],tot=-1,hehe;int rson[160100],lson[160100],treepoint=1;int ch[161000];queue<int> q;void add(int x,int y,int z){    tot++;    nextt[tot]=head[x];    head[x]=tot;    ver[tot]=y;    edge[tot]=z;}bool tell(){    q.push(0);    memset(ch,-1,sizeof ch);    ch[0] = 0;    while (q.size())    {        int x = q.front();q.pop();        for (int i = head[x];i!=-1;i=nextt[i])            if (ch[ver[i]]==-1&&edge[i])                ch[ver[i]]=ch[x]+1,q.push(ver[i]);    }    return ch[treepoint+n+1]!=-1;}int zeng(int a,int b){    if (a == treepoint+n+1) return b;    int r = 0;    for (int i = head[a];i!=-1;i=nextt[i])    if (ch[ver[i]] == ch[a]+1&&edge[i])    {        int t = zeng(ver[i],min(b-r,edge[i]));        r+=t;edge[i]-=t,edge[i^1]+=t;    }    if (!r) ch[a]=-1;    return r;}int judge(int x){    for (int i = 0;i <= tot;i+=2)        edge[i] += edge[i^1],edge[i^1]=0;    for (int i = hehe+1;i <= tot;i+=2)        edge[i] = x;    int r = 0,z;    while (tell())        while (z = zeng(0,0x3f3f3f3f))            r+=z;    return r;}void maketree(int x,int l,int r){    if (l == r) return ;    int mid = (l + r)/2;    lson[x] = ++treepoint;    rson[x] = ++treepoint;    maketree(lson[x],l,mid);    maketree(rson[x],mid+1,r);}void maketree2(int x,int l,int r){    int mid = (l + r)/2;    if (l == r) {        add(x,treepoint+n+1,1),add(treepoint+n+1,x,0);return ;    }    add(x,lson[x],mid-l+1),add(lson[x],x,0);    add(x,rson[x],r-mid),add(rson[x],x,0);    maketree2(lson[x],l,mid);    maketree2(rson[x],mid+1,r);}void add(int x,int l,int r,int ll,int rr,int hehe){    if (l > rr || r < ll) return ;    if (ll <= l && r <= rr)         {            add(treepoint+hehe,x,r-l+1);            add(x,treepoint+hehe,0);            return ;        }    int mid = (l + r)/2;    add(lson[x],l,mid,ll,rr,hehe);    add(rson[x],mid+1,r,ll,rr,hehe);}int main(){    memset(head,-1,sizeof head);    cin >> n;maxx = 10000/n;    maketree(1,1,10000);    maketree2(1,1,10000);    for (int i = 1;i <= n;i++)    {        int x,y;scanf("%d%d",&x,&y);y--;x++,y++;maxx = min(maxx,(y-x+1));        add(1,1,10000,x,y,i);    }    hehe = tot;    for (int i = 1;i <= n;i++) add(0,treepoint+i,0),add(treepoint+i,0,0);    int l = 0,r = maxx+1;    while (l < r)    {        int mid = (l + r)/2;        if (judge(mid)==mid*n) l = mid + 1;        else r = mid;    }    cout << (l-1)*n << endl;}