BestCoder Round #74 (div.2 d) hdu5638 Toposort 【线段树】

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链接：http://acm.hdu.edu.cn/showproblem.php?pid=5638

题意：给出n个点m条边的有向无环图. 要求删掉恰好k条边使得字典序最小的拓扑序列尽可能小.

分析：因为要字典序最小，所以每次要找入度小于等于k的最小节点，用线段树维护即可。

#include<algorithm>#include<iostream>#include<cstring>#include<cstdio>#include<string>#include<vector>#include<queue>#include<cmath>#include<stack>#include<set>#include<map>#define INF 0x3f3f3f3f#define Mn 100010#define Mm 200005#define mod 1000000007#define CLR(a,b) memset((a),(b),sizeof((a)))#define CPY(a,b) memcpy ((a), (b), sizeof((a)))#pragma comment(linker, "/STACK:102400000,102400000")#define ul u<<1#define ur (u<<1)|1using namespace std;typedef long long ll;int read() {    char c=getchar();    int re=0,f=1;    while(c<'0'||c>'9') {if(c=='-') f=-1;c=getchar();}    while(c>='0'&&c<='9') {re=re*10+c-'0';c=getchar();}    return re;}struct edge {    int next,v;}e[Mm];int head[Mn],tot;void addedge(int u,int v) {    e[tot].v=v;    e[tot].next=head[u];    head[u]=tot++;}void init() {    CLR(head,-1);    tot=0;}int minn[Mn*4];int degree[Mn];void push_up(int u) {    minn[u]=min(minn[ul],minn[ur]);}void build(int l,int r,int u) {    if(l==r) {        minn[u]=degree[l];        return ;    }    int mid=(l+r)>>1;    build(l,mid,ul);    build(mid+1,r,ur);    push_up(u);}void update(int pos,int l,int r,int u,int x) {    if(l==r) {        minn[u]+=x;        return ;    }    int mid=(l+r)>>1;    if(pos<=mid) update(pos,l,mid,ul,x);    else update(pos,mid+1,r,ur,x);    push_up(u);}int query(int l,int r,int u,int &k) {    if(l==r) {        k-=minn[u];        if(k<0) k=0;        return l;    }    int mid=(l+r)>>1;    if(k>=minn[ul]) return query(l,mid,ul,k);    else return query(mid+1,r,ur,k);}int main() {    int t=read();    while(t--) {        init();        CLR(degree,0);        int n=read(),m=read(),k=read();        for(int i=1;i<=m;i++) {            int u=read(),v=read();            addedge(u,v);            degree[v]++;        }        build(1,n,1);        ll sum=0;        for(int i=1;i<=n;i++) {            int u=query(1,n,1,k);            update(u,1,n,1,INF);            for(int j=head[u];~j;j=e[j].next) {                int v=e[j].v;                update(v,1,n,1,-1);            }            sum=(sum+((ll)i*u)%mod)%mod;        }        cout<<sum<<endl;    }    return 0;}

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