【BZOJ1016】[JSOI2008]最小生成树计数【最小生成树】【搜索】

来源：互联网发布：wto贸易数据库编辑：程序博客网时间：2024/05/02 01:12

【题目链接】

参考了【hzwer的题解】orz

要利用最小生成树的性质：对于所有的最小生成树，边权相等的边出现次数都相同。

/* Footprints In The Blood Soaked Snow */#include <cstdio>#include <algorithm>using namespace std;const int maxn = 105, maxm = 1005, p = 31011;int n, m, fa[maxn], tot, sum, ans;struct _edge {int u, v, w;} g[maxm];struct _data {int cnt, l, r;} e[maxm];inline int iread() {int f = 1, x = 0; char ch = getchar();for(; ch < '0' || ch > '9'; ch = getchar()) f = ch == '-' ? -1 : 1;for(; ch >= '0' && ch <= '9'; ch = getchar()) x = x * 10 + ch - '0';return f * x;}inline int find(int x) {return fa[x] == x ? x : find(fa[x]);}inline bool cmp(_edge a, _edge b) {return a.w < b.w;}inline void dfs(int now, int id, int used) {if(now == e[id].r + 1) {if(used == e[id].cnt) sum++;return;}int u = find(g[now].u), v = find(g[now].v);if(u != v) {fa[u] = v;dfs(now + 1, id, used + 1);fa[u] = u; fa[v] = v;}dfs(now + 1, id, used);}int main() {n = iread(); m = iread();for(int i = 1; i <= m; i++) {int u = iread(), v = iread(), w = iread();g[i] = (_edge){u, v, w};}for(int i = 1; i <= n; i++) fa[i] = i;sort(g + 1, g + 1 + m, cmp);int flag = 0;for(int i = 1; i <= m; i++) {if(g[i - 1].w != g[i].w) {e[tot].r = i - 1; ++tot;e[tot].l = i;}int u = find(g[i].u), v = find(g[i].v);if(u != v) {e[tot].cnt++;fa[u] = v;flag++;}}e[tot].r = m;if(flag != n - 1) {printf("0\n");return 0;}for(int i = 1; i <= n; i++) fa[i] = i;ans = 1;for(int i = 1; i <= tot; i++) {if(e[i].cnt) {sum = 0;dfs(e[i].l, i, 0);} else sum = 1;ans = ans * sum % p;for(int j = e[i].l; j <= e[i].r; j++) {int u = find(g[j].u), v = find(g[j].v);fa[u] = v;}}printf("%d\n", ans);return 0;}

0 0