题目链接如下：
这道题也是看了刘汝佳的思路才写出来的....
代码如下：
cpp
#include <cstdio>
#include <deque>
#include <vector>
#include <algorithm>
#include <map>
const int maxx = 100005;
const int maxColor = 1e9 + 1;
// #define debug
struct node{
int id, color;
node(int _id, int _color): id(_id), color(_color){}
};
int n, m, u, v, c, k, curr, minn;
std::map<int, std::vector<node>> mp;
int d[maxx], pre[maxx], preColor[maxx];
bool vis[maxx];
void bfs1(){
std::deque<int> dq;
dq.push_back(n);
d[n] = 0;
vis[n] = true;
while (!dq.empty()){
curr = dq.front();
dq.pop_front();
for (int i = 0; i < mp[curr].size(); ++i){
int temp = mp[curr][i].id;
if (!vis[temp]){
d[temp] = d[curr] + 1;
vis[temp] = true;
dq.push_back(temp);
}
}
}
}
void bfs2(){
std::deque<int> dq;
dq.push_back(1);
while (!dq.empty()){
curr = dq.front();
dq.pop_front();
minn = maxColor;
for (int i = 0; i < mp[curr].size(); ++i){
int temp = mp[curr][i].id;
if (d[temp] == d[curr] - 1){
minn = std::min(minn, mp[curr][i].color);
}
}
for (int i = 0; i < mp[curr].size(); ++i){
int temp = mp[curr][i].id;
if (d[temp] == d[curr] - 1 && mp[curr][i].color == minn){
if (!pre[temp]){
dq.push_back(temp);
}
if (!pre[temp] || preColor[temp] > minn){
pre[temp] = curr;
preColor[temp] = minn;
}
}
}
}
}
int main(){
#ifdef debug
freopen("0.txt", "r", stdin);
freopen("1.txt", "w", stdout);
#endif
while (scanf("%d %d", &n, &m) == 2){
mp.clear();
std::fill(d, d + n + 1, -1);
std::fill(vis, vis + n + 1, false);
std::fill(pre, pre + n + 1, 0);
std::fill(preColor, preColor + n + 1, -1);
while (m--){
scanf("%d %d %d", &u, &v, &c);
if (u != v){
mp[u].push_back(node(v, c));
mp[v].push_back(node(u, c));
}
}
bfs1();
bfs2();
std::vector<int> path;
curr = n;
do {
path.push_back(preColor[curr]);
curr = pre[curr];
} while (curr != 1);
reverse(path.begin(), path.end());
printf("%d\n", path.size());
for (int i = 0; i < path.size(); ++i){
printf("%d%s", path[i], i == path.size() - 1 ? "\n" : " ");
}
}
#ifdef debug
fclose(stdin);
fclose(stdout);
#endif
return 0;
}