比赛 |
CSP2023-S模拟赛 |
评测结果 |
AAAAAAEAAA |
题目名称 |
编辑题目 |
最终得分 |
90 |
用户昵称 |
HzmQwQ |
运行时间 |
3.456 s |
代码语言 |
C++ |
内存使用 |
121.13 MiB |
提交时间 |
2023-10-17 21:48:44 |
显示代码纯文本
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <vector>
#include <stack>
#define MAXN 1000005
#define min(x, y) ((x) < (y) ? (x) : (y))
#define max(x, y) ((x) > (y) ? (x) : (y))
using namespace std;
typedef long long ll;
struct edge {
int u, v, w;
} Edge[MAXN];
struct node {
int to, wgt;
};
const ll M = 998244353LL;
int n, m, wt[MAXN], dfn[MAXN], low[MAXN], dfncnt, scc[MAXN], vwt[MAXN], scccnt, son_sz[MAXN], dfnT[MAXN], dfnTcnt, mxdfT[MAXN];
bool instack[MAXN];
vector <node> G[MAXN];
vector <int> swe[MAXN], T[MAXN];
stack <int> st;
int tmpdfn[MAXN];
int qread() {
int x = 0;
char c = getchar();
while(c < '0' || c > '9') c = getchar();
while(c >= '0' && c <= '9') {
x = 10 * x + c - '0';
c = getchar();
}
return x;
}
ll quick_pow(ll base, ll xp) {
ll ret = 1LL;
while(xp > 0) {
if(xp & 1LL) ret = (ret * base) % M;
base = (base * base) % M;
xp >>= 1LL;
}
return ret;
}
void tarjan(int u, int fr) {
dfn[u] = low[u] = ++dfncnt;
st.push(u);
instack[u] = true;
for(node nxt : G[u]) {
int v = nxt.to;
if(v == fr) continue;
if(dfn[v] == 0) {
tarjan(v, u);
low[u] = min(low[u], low[v]);
}
else if(instack[v]) low[u] = min(low[u], dfn[v]);
}
if(low[u] == dfn[u]) {
++scccnt;
while(st.top() != u) {
scc[st.top()] = scccnt;
++vwt[scccnt];
instack[st.top()] = false;
st.pop();
}
scc[st.top()] = scccnt;
++vwt[scccnt];
instack[st.top()] = false;
st.pop();
}
return ;
}
void getTr() {
for(int i = 1; i <= m; i++) {
if(scc[Edge[i].u] == scc[Edge[i].v]) continue;
T[scc[Edge[i].u]].push_back(scc[Edge[i].v]);
T[scc[Edge[i].v]].push_back(scc[Edge[i].u]);
}
return ;
}
void dfsTr(int u, int fr) {
dfnT[u] = ++dfnTcnt;
son_sz[dfnT[u]] = vwt[u];
mxdfT[dfnT[u]] = dfnT[u];
for(int v : T[u]) {
if(v == fr) continue;
dfsTr(v, u);
son_sz[dfnT[u]] += son_sz[dfnT[v]];
mxdfT[dfnT[u]] = max(mxdfT[dfnT[u]], mxdfT[dfnT[v]]);
}
return ;
}
int main() {
freopen("edit.in", "r", stdin);
freopen("edit.out", "w", stdout);
n = qread(); m = qread();
for(int i = 1; i <= m; i++) {
Edge[i].u = qread(); Edge[i].v = qread(); Edge[i].w = qread();
wt[i] = Edge[i].w;
}
sort(wt + 1, wt + m + 1);
int ulen = unique(wt + 1, wt + m + 1) - wt - 1;
for(int i = 1; i <= m; i++) {
int pos = lower_bound(wt + 1, wt + ulen + 1, Edge[i].w) - wt;
Edge[i].w = pos;
swe[pos].push_back(i);
G[Edge[i].u].push_back((node){Edge[i].v, Edge[i].w});
G[Edge[i].v].push_back((node){Edge[i].u, Edge[i].w});
}
tarjan(1, 0);
ll fr = quick_pow((ll)m, M - 2LL);
ll frn = quick_pow((ll)n, M - 2LL);
getTr();
dfsTr(1, 0);
ll ans = 0LL;
for(int i = 1; i <= ulen; i++) {
if(swe[i].size() == 1) continue;
else {
int slen = swe[i].size(), tlen = 0;
for(int j = 0; j < swe[i].size(); j++) {
int ed = swe[i][j];
if(scc[Edge[ed].u] == scc[Edge[ed].v]) {
ans = (ans + (ll)n) % M;
tmpdfn[++tlen] = dfnT[scc[Edge[ed].u]];
continue;
}
tmpdfn[++tlen] = dfnT[scc[Edge[ed].u]];
tmpdfn[++tlen] = dfnT[scc[Edge[ed].v]];
}
sort(tmpdfn + 1, tmpdfn + tlen + 1);
for(int ed : swe[i]) {
if(scc[Edge[ed].u] == scc[Edge[ed].v]) continue;
int fad = min(dfnT[scc[Edge[ed].u]], dfnT[scc[Edge[ed].v]]), snd = max(dfnT[scc[Edge[ed].u]], dfnT[scc[Edge[ed].v]]);
int mxs = mxdfT[snd];
int pos1 = upper_bound(tmpdfn + 1, tmpdfn + tlen + 1, mxs) - tmpdfn;
int pos2 = lower_bound(tmpdfn + 1, tmpdfn + tlen + 1, snd) - tmpdfn;
int sz = pos1 - pos2 + 1;
if(sz > 2) ans = (ans + (ll)son_sz[snd]);
if(sz < tlen) ans = (ans + (ll)n - (ll)son_sz[snd]);
}
for(int j = 1; j <= tlen; j++) tmpdfn[j] = 0;
}
}
printf("%lld\n", (((ans * fr) % M) * frn) % M);
return 0;
}