POJ 3177Redundant Paths 边双连通分量

来源：互联网发布：自贡广电网络编辑：程序博客网时间：2024/06/01 13:20

题目：http://poj.org/problem?id=3177

题意：跟3352一样，最少加多少条边使图变得双连通，唯一的区别是此题会有重边，需要判重

思路：我自己写的判重挺搓的，直接用一个5000*5000的bool标记数组，虽然过了，总感觉不好，于是看了大神的判重，改了一下，代码是改过后的

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <vector>using namespace std;const int N = 5010;struct edge{    int to, next;} G[N*5];int dfn[N], low[N], st[N], dcc[N], head[N];int index, num, cnt, top;bool vis[N];int n, m;void init(){    memset(dfn, -1, sizeof dfn);    memset(head, -1, sizeof head);    memset(vis, 0, sizeof vis);    index = num = cnt = top = 0;}void add_edge(int v, int u){    G[cnt].to = u;    G[cnt].next = head[v];    head[v] = cnt++;}bool judge(int v, int fa)/*判重边*/{    int tmp = 0;    for(int i = head[v]; i != -1; i = G[i].next)        if(G[i].to == fa) tmp++;    if(tmp >= 2) return true;    else return false;}void tarjan(int v, int fa){    dfn[v] = low[v] = index++;    vis[v] = true;    st[top++] = v;    bool f = judge(v, fa);    int u, t;    for(int i = head[v]; i != -1; i = G[i].next)    {        u = G[i].to;        if(u == fa && ! f) continue;/*此处条件稍变*/        if(dfn[u] == -1)        {            tarjan(u, v);            low[v] = min(low[v], low[u]);            if(dfn[v] < low[u])            {                num++;                do                {                    t = st[--top];                    vis[t] = false;                    dcc[t] = num;                }                while(t != u);            }        }        else if(vis[u])            low[v] = min(low[v], dfn[u]);    }}void slove(){    tarjan(1, -1);    int deg[N];    memset(deg, 0, sizeof deg);    for(int i = 1; i <= n; i++)        for(int j = head[i]; j != -1; j = G[j].next)            if(dcc[i] != dcc[G[j].to])                deg[dcc[i]]++;    int res = 0;    for(int i = 0; i <= num; i++)        if(deg[i] == 1) res++;    printf("%d\n", (res + 1) / 2);}int main (){    int a, b;    while(~ scanf("%d%d", &n, &m))    {        init();        for(int i = 0; i < m; i++)        {            scanf("%d%d", &a, &b);            add_edge(a, b);            add_edge(b, a);        }        slove();    }    return 0;}

0 0