题目链接：http://poj.org/problem?id=2117
题意：求去掉割点后的最大连通分支个数。
kuangbin的板子。
1 #include <algorithm> 2 #include <iostream> 3 #include <iomanip> 4 #include <cstring> 5 #include <climits> 6 #include <complex> 7 #include <cassert> 8 #include <cstdio> 9 #include <bitset> 10 #include <vector> 11 #include <deque> 12 #include <queue> 13 #include <stack> 14 #include <ctime> 15 #include <set> 16 #include <map> 17 #include <cmath> 18 using namespace std; 19 20 const int maxn = 10050; 21 typedef struct Edge { 22 int u; 23 int v; 24 int next; 25 Edge() { next = -1; } 26 }Edge; 27 28 int head[maxn], ecnt; 29 Edge edge[maxn<<2]; 30 int n, m; 31 int del; 32 33 int dindex; 34 int dfn[maxn], low[maxn]; 35 int stk[maxn], top; 36 int belong[maxn]; 37 bool instk[maxn]; 38 39 void init() { 40 memset(edge, 0, sizeof(edge)); 41 memset(head, -1, sizeof(head)); 42 memset(instk, 0, sizeof(instk)); 43 memset(dfn, 0, sizeof(dfn)); 44 memset(low, 0, sizeof(low)); 45 memset(belong, 0, sizeof(belong)); 46 ecnt = top = dindex = 0; 47 } 48 49 void adde(int uu, int vv) { 50 edge[ecnt].u = uu; 51 edge[ecnt].v = vv; 52 edge[ecnt].next = head[uu]; 53 head[uu] = ecnt++; 54 } 55 56 void tarjan(int u, int pre) { 57 int v; 58 dfn[u] = low[u] = ++dindex; 59 stk[top++] = u; 60 instk[u] = 1; 61 int son = 0; 62 for(int i = head[u]; ~i; i=edge[i].next) { 63 v = edge[i].v; 64 if(v == pre) continue; 65 // if(v == del || v == pre) continue; 66 if(!dfn[v]) { 67 son++; 68 tarjan(v, u); 69 low[u] = min(low[u], low[v]); 70 if(u != pre && low[v] >= dfn[u]) belong[u]++; 71 } 72 else low[u] = min(low[u], dfn[v]); 73 } 74 if(u == pre) belong[u] = son - 1; 75 instk[u] = 0; 76 top--; 77 } 78 79 80 int main() { 81 // freopen("in", "r", stdin); 82 int u, v; 83 while(~scanf("%d%d",&n,&m) && n + m) { 84 init(); 85 for(int i = 0; i < m; i++) { 86 scanf("%d %d", &u, &v); 87 u++; v++; 88 adde(u, v); adde(v, u); 89 } 90 int ret = 0; 91 // for(int i = 1; i <= n; i++) { 92 // del = i; 93 memset(instk, 0, sizeof(instk)); 94 memset(dfn, 0, sizeof(dfn)); 95 memset(belong, 0, sizeof(belong)); 96 top = dindex = 0; 97 int cnt = 0; 98 for(int j = 1; j <= n; j++) { 99 // if(j == del) continue; 100 if(!dfn[j]) { 101 tarjan(j, j); 102 cnt++; 103 } 104 } 105 for(int j = 1; j <= n; j++) { 106 ret = max(ret, cnt+belong[j]); 107 } 108 // } 109 printf("%d ", ret); 110 } 111 return 0; 112 }