# 洛谷 [P1608] 最短路计数

## 最短路计数模版

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstdlib>
#include <cmath>
#include <queue>
#include <cstring>
using namespace std;
const int MAXN = 2005;
int head[MAXN], n, m, nume, dist[MAXN], cnt[MAXN];
bool f[MAXN];
struct edge{
int to, nxt, dis;
}e[MAXN * MAXN];
void adde(int from, int to, int dis) {
e[++nume].to = to;
e[nume].dis = dis;
}
int init() {
int rv = 0, fh = 1;
char c = getchar();
while(c < '0' || c > '9') {
if(c == '-') fh = -1;
c = getchar();
}
while(c >= '0' && c <= '9') {
rv = (rv<<1) + (rv<<3) + c - '0';
c = getchar();
}
return fh * rv;
}
struct node{
int num, dis;
bool operator < (const node & b) const{
return dis > b.dis;
}
}a[MAXN];
priority_queue <node> q;
void dij() {
memset(dist, 0x3f, sizeof(dist));
dist[1] = 0;
q.push((node){1, 0});
while(!q.empty()) {
node u = q.top(); q.pop();
if(f[u.num]) continue;
f[u.num] = 1;
for(int i = head[u.num]; i; i = e[i].nxt) {
node v;
v.num = e[i].to;
if(dist[v.num] > dist[u.num] + e[i].dis) {
dist[v.num] = dist[u.num] + e[i].dis;
v.dis = dist[v.num];
q.push(v);
}
}
}
}
void cnnt() {
memset(f, 0, sizeof(f));
for(int i = 1; i <= n; i++) a[i] = (node) {i, dist[i]};
sort(a + 1, a + n + 1);
cnt[1] = 1;
for(int i = n; i >= 1; i--) {
int u = a[i].num;
for(int i = head[u]; i; i = e[i].nxt) {
int v = e[i].to;
if(dist[v] == dist[u] + e[i].dis) {
cnt[v] += cnt[u];
}
}
}
}
int ddd[MAXN][MAXN];
int main() {
n = init(); m = init();
memset(ddd, 0x3f, sizeof(ddd));
for(int i = 1; i <= m; i++) {
int u = init(), v = init(), dis = init();
ddd[u][v] = min(ddd[u][v], dis);
}
for(int i = 1; i <= n; i++) {
for(int j = 1; j <= n; j++) {
if(ddd[i][j] != 0x3f3f3f3f) adde(i, j, ddd[i][j]);
}
}
dij();
cnnt();
}