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上一篇 :
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1 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 ; }
#include#include #include #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; else link_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; }