UVA 315【求割点数目】

https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=251

题意：求割点数目

代码：

#include <stdio.h>
#include <ctime>
#include <math.h>
#include <limits.h>
#include <complex>
#include <string>
#include <functional>
#include <iterator>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <list>
#include <bitset>
#include <sstream>
#include <iomanip>
#include <fstream>
#include <iostream>
#include <ctime>
#include <cmath>
#include <cstring>
#include <cstdio>
#include <time.h>
#include <ctype.h>
#include <string.h>
#include <assert.h>
#pragma comment (linker, "/STACK:102400000,102400000")

using namespace std;

int n, m, x, y;

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];
            //桥
            //一条无向边(u,v)是桥，当且仅当(u,v)为树枝边，且满足DFS(u)<Low(v)。
            if (Low[v] > DFN[u])
            {
                bridge++;
                edge[i].cut = true;
                edge[i ^ 1].cut = true;
            }
            //割点
            //一个顶点u是割点，当且仅当满足(1)或(2) (1) u为树根，且u有多于一个子树。
            //(2) u不为树根，且满足存在(u,v)为树枝边(或称父子边，
            //即u为v在搜索树中的父亲)，使得DFS(u)<=Low(v)
            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];
    }
    //树根，分支数大于1
    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);
    int ans = 0;
    for (int i = 1; i <= N; i++)
        if (cut[i])
            ans++;
    printf("%d\n", ans);
}

void init()
{
    tot = 0;
    memset(head, -1, sizeof(head));
}

int main()
{
    while (~scanf("%d", &n) && n)
    {
        init();
        while (scanf("%d", &m) && m)
        {
            while (getchar() != ‘\n‘)
            {
                scanf("%d", &x);
                addedge(m, x);
                addedge(x, m);
            }
        }
        solve(n);
    }
    return 0;
}

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