poj1523 SPF【求割点，Targan算法】

解题报告参考《图论算法理论、实现及应用》 P390

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;

const int MAXN = 1000 + 10;

int Edge[MAXN][MAXN];
int visited[MAXN];
int dfn[MAXN];
int low[MAXN];
int subnets[MAXN];
int nodes; //顶点数目。
int tmpdfn; //在dfs过程中记录当前的深度优先搜索序数。
int son; //根节点的子女节点的个数(如果大于2，则根节点是关节点).

void dfs(int u)
{
    for(int v = 1; v <= nodes; v++) {
        if( Edge[u][v] ) {
            if( !visited[v] ) {
                visited[v] = 1;
                tmpdfn++;
                dfn[v] = low[v] = tmpdfn;
                dfs( v );
                low[u] = min(low[u], low[v]);
                if(low[v] >= dfn[u]) {
                    if(u != 1) {
                        subnets[u]++;
                    }
                    if(u == 1) {
                        son++;
                    }
                }
            } else {
                low[u] = min(low[u], dfn[v]);
            }
        }
    }
}

void init()
{
    low[1] = dfn[1] = 1;
    tmpdfn = 1; son = 0;
    memset(visited, 0, sizeof(visited));
    visited[1] = 1;
    memset(subnets, 0, sizeof(subnets));
}

int main()
{
    int T = 1;
    while(1) {
        memset(Edge, 0, sizeof(Edge));
        int u, v;
        scanf("%d", &u);
        if(u == 0) break;
        nodes = 0;
        scanf("%d", &v);
        if(u > nodes) nodes = u;
        if(v > nodes) nodes = v;
        Edge[u][v] = Edge[v][u] = 1;
        while(1) {
            scanf("%d", &u);
            if(u == 0) break;
            scanf("%d", &v);
            if(u > nodes) nodes = u;
            if(v > nodes) nodes = v;
            Edge[u][v] = Edge[v][u] = 1;
        }
        if(T > 1) printf("\n");
        printf("Network #%d\n", T++);
        init();
        dfs(1);
        if(son > 1) subnets[1] = son - 1;
        int find = 0;
        for(int i = 1; i <= nodes; i++) {
            if(subnets[i]) {
                find = 1;
                printf("  SPF node %d leaves %d subnets\n", i, subnets[i]+1);
            }
        }
        if(!find) printf("  No SPF nodes\n");
    }
    return 0;
}