求割点（邻接表无向图）C~

上一篇 ： 图割点（邻接矩阵）

邻接表 ： O(N+M)

邻接矩阵 : O(N^2)

核心代码 ： 

void dfs(int cur, int father, Graph g, Info* info){info->index++;info->num[cur] = info->index;info->low[cur] = info->index;info->child = 0;//记录每个顶点孩子数量 ENode *node;node = g.vex[cur].first_edge;while(node != NULL){ //访问 每个 临接点 if(info->num[node->ivex] == 0){//当前顶点未访问info->child++;//当前顶点孩子数加1dfs(node->ivex, cur, g, info);//info->low[cur] = min(info->low[cur], info->low[node->ivex]);if(info->root != cur && info->low[node->ivex] >= info->num[cur] ){info->flag[cur] = 1;info->cnt++;}if(info->root == cur && info->child == 2){info->flag[cur] = 1;info->cnt++;}}else if(node->ivex != father){info->low[cur] = min(info->low[cur], info->num[node->ivex]);}node = node->next_edge;}return ;}

完整实现 ： 

#include<stdio.h>#include<stdlib.h>#include<ctype.h>#define MAXVEX 100 typedef char VertexType;  typedef int WeightType;  typedef struct ENode {      int ivex;//顶点 索引        WeightType weight;      struct ENode* next_edge;  }ENode;  typedef struct Info{// 记录  int index;int root;int child;int num[MAXVEX];//当前顶点的时间戳 int low[MAXVEX];//能访问到的最早顶点的时间戳 int flag[MAXVEX];int cnt;}Info;  typedef struct VNode {      VertexType data; // 顶点 信息        ENode* first_edge;  }VNode;    typedef struct Graph {      VNode vex[MAXVEX];      int vex_num, edge_num;  }Graph;  int index;char read_char()  {      char ch;      do {          ch = getchar();      } while (!isalpha(ch));      return ch;  }    int get_pos(Graph g, char ch)  {      int i;      for (i = 0; i < g.vex_num; i++) {          if (ch == g.vex[i].data)              return i;      }        return -1;  }    void link_last(ENode* list, ENode *last)  {      ENode* p;      p = list;      while (p->next_edge != NULL) {          p = p->next_edge;      }      p->next_edge = last;  }  void create_graph(Graph *g)  {      int i, w;      printf("请输入顶点数和边数:\n");      scanf("%d%d", &g->vex_num, &g->edge_num);      printf("请输入顶点信息:\n");      for (i = 0; i < g->vex_num; i++) {          g->vex[i].first_edge = NULL;          g->vex[i].data = read_char();      }      printf("请输入边 :\n");      for (i = 0; i < g->edge_num; i++) {          int p1, p2;          char c1, c2;          c1 = read_char();          c2 = read_char();      //    scanf("%d", &w);          p1 = get_pos(*g, c1);          p2 = get_pos(*g, c2);          ENode* node1, *node2;          node1 = (ENode*)malloc(sizeof(ENode));          if (node1 == NULL) {              printf("error");              return;          }          node1->next_edge = NULL;          node1->ivex = p2;            if (g->vex[p1].first_edge == NULL)              g->vex[p1].first_edge = node1;          else              link_last(g->vex[p1].first_edge, node1);node2 = (ENode *)malloc(sizeof(ENode));  node2->next_edge = NULL;node2->ivex = p1;        if(g->vex[p2].first_edge == NULL)g->vex[p2].first_edge = node2; elselink_last(g->vex[p2].first_edge, node2);       }  } int min(int a, int b){return a < b ? a : b;}// 求割点核心void dfs(int cur, int father, Graph g, Info* info){info->index++;info->num[cur] = info->index;info->low[cur] = info->index;info->child = 0;//记录每个顶点孩子数量 ENode *node;node = g.vex[cur].first_edge;while(node != NULL){ //访问 每个 临接点 if(info->num[node->ivex] == 0){info->child++;dfs(node->ivex, cur, g, info);info->low[cur] = min(info->low[cur], info->low[node->ivex]);if(info->root != cur && info->low[node->ivex] >= info->num[cur] ){info->flag[cur] = 1;info->cnt++;}if(info->root == cur && info->child == 2){info->flag[cur] = 1;info->cnt++;}}else if(node->ivex != father){info->low[cur] = min(info->low[cur], info->num[node->ivex]);}node = node->next_edge;}return ;}int main(){Graph g;create_graph(&g);Info info;info.index = 0;info.root = 0;int i;for(int i = 0; i < g.vex_num; i++ ){info.num[i] = 0;// 这个必须初始化 为 0 表示未访问 info.cnt = 0;}dfs(0, 0, g, &info);if(info.cnt == 0){printf("\n该图不存在割点");return 0;}printf("\n此图有%d个割点 : ",info.cnt);for(i = 0; i < g.vex_num; i++ ){if(info.flag[i] == 1)printf("%c ", g.vex[i].data);}return 0;}