UVA 796 Critical Links（求桥）

来源：互联网发布：linux 编译器gdb 编辑：程序博客网时间：2024/05/17 22:05
可以找出割点和桥，求删掉每个点后增加的连通块。
需要注意重边的处理，可以先用矩阵存，再转邻接表，或者进行判重
#include<stdio.h>#include<stdlib.h>#include<string.h>#include<stack>#include<algorithm>#include<vector>#include<map>using namespace std;const int MAXN = 10010;const int MAXM = 100010;struct Edge{    int to,next;    bool cut;//是否为桥的标记} edge[MAXM];int head[MAXN],tot;int Low[MAXN],DFN[MAXN],Stack[MAXN];int Index,top;bool Instack[MAXN];bool cut[MAXN];int add_block[MAXN];//删除一个点后增加的连通块int bridge;void addedge(int u,int v){    edge[tot].to = v;    edge[tot].next = head[u];    edge[tot].cut = false;    head[u] = tot++;}void Tarjan(int u,int pre){    int v;    Low[u] = DFN[u] = ++Index;    Stack[top++] = u;    Instack[u] = true;    int son = 0;    for(int i = head[u]; i != -1; i = edge[i].next)    {        v = edge[i].to;        if(v == pre)continue;        if( !DFN[v] )        {            son++;            Tarjan(v,u);            if(Low[u] > Low[v])Low[u] = Low[v];            if(Low[v] > DFN[u])            {                bridge++;                edge[i].cut = true;                edge[i^1].cut = true;            }            if(u != pre && Low[v] >= DFN[u])//不是树根            {                cut[u] = true;                add_block[u]++;            }        }        else if( Low[u] > DFN[v])            Low[u] = DFN[v];    }    if(u == pre && son > 1)cut[u] = true;    if(u == pre)add_block[u] = son - 1;    Instack[u] = false;    top--;}void solve(int N){    memset(DFN,0,sizeof(DFN));    memset(Instack,false,sizeof(Instack));    memset(add_block,0,sizeof(add_block));    memset(cut,false,sizeof(cut));    Index = top = 0;    bridge = 0;    for(int i = 1; i <= N; i++)        if( !DFN[i] )            Tarjan(i,i);    printf("%d critical links\n",bridge);    vector<pair<int,int> >ans;    for(int u = 1; u <= N; u++)        for(int i = head[u]; i != -1; i = edge[i].next)            if(edge[i].cut && edge[i].to > u)            {                ans.push_back(make_pair(u,edge[i].to));            }    sort(ans.begin(),ans.end());    for(int i = 0; i < ans.size(); i++)        printf("%d - %d\n",ans[i].first-1,ans[i].second-1);    printf("\n");}void init(){    tot = 0;    memset(head,-1,sizeof(head));}map<int,int>mapit;inline bool isHash(int u,int v){    if(mapit[u*MAXN+v])return true;    if(mapit[v*MAXN+u])return true;    mapit[u*MAXN+v] = mapit[v*MAXN+u] = 1;    return false;}int main(){    int n;    while(scanf("%d",&n) == 1)    {        init();        int u;        int k;        int v;        for(int i = 1; i <= n; i++)        {            scanf("%d (%d)",&u,&k);            u++;            while(k--)            {                scanf("%d",&v);                v++;                if(v <= u)continue;                addedge(u,v);                addedge(v,u);            }        }        solve(n);    }    return 0;}
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