rt，60pts，The path does not lead to the end vertex.

没想出来 思路变量名几乎和题解相同

#include<cstdio>
#include<cctype>
#include<queue>
#include<vector>
#include<cstring>
#include<algorithm>
#define R register
#define INF (0x3f3f3f3f)
using namespace std;

char buf[200005], *p1 = buf, *p2 = buf;
#define getchar() (p1==p2&&(p2=(p1=buf)+fread(buf,1,200000,stdin),p1==p2)?EOF:*p1++)
inline int read() {
	int x = 0; char c = getchar();
	while (!isdigit(c)) c = getchar();
	while (isdigit(c)) x = (x << 3) + (x << 1) + (c ^ 48), c = getchar();
	return x;
}

const int MAXN = 405;

int n, m, Q;
int f[MAXN][MAXN], g[MAXN][MAXN][27];
vector<int>to[MAXN][27], pre[MAXN][27];
struct Link {
	int l, r, c;
}pf[MAXN][MAXN], pg[MAXN][MAXN][27];
queue<Link>q1, q2;

int ans[MAXN];
inline void Output(int x, int y) {
	int l = 0, r = f[x][y] + 1, len = f[x][y], c, t1, t2;
	printf ("%d ", f[x][y]);
	while (l + 1 < r) {
		ans[++ l] = (c = pf[x][y].c);
		t1 = x, t2 = y;
		x = pf[t1][t2].l, y = pf[t1][t2].r;
		if (l + 1 >= r) break;
		ans[-- r] = c;
		t1 = x, t2 = y;
		x = pg[t1][t2][c].l, y = pg[t1][t2][c].r;
	}
	for (R int i = 1; i <= len; ++ i) putchar(ans[i] + 'a');
	puts("");
}

int main()
{
	n = read(), m = read();
	memset(f, 0x3f, sizeof(f));
	memset(g, 0x3f, sizeof(g));
	for (R int i = 1; i <= n; ++ i)
		f[i][i] = 0, q1.push((Link){i, i, 0});
	char cc; int x, y, w; 
	for (R int i = 1; i <= m; ++ i) {
		x = read(), y = read(), cc = getchar();
		while (cc < 'a' && cc > 'z') cc = getchar();
		w = cc - 'a';
		to[x][w].push_back(y);
		pre[y][w].push_back(x);
		f[x][y] = 1; pf[x][y] = (Link){0, 0, w};
		q1.push((Link){x, y, 0}); 
	}
	while (!q1.empty() || !q2.empty()) {
		if (!q1.empty() && (q2.empty() || f[q1.front().l][q1.front().r] <= g[q2.front().l][q2.front().r][q2.front().c])) {
			x = q1.front().l, y = q1.front().r;
			q1.pop();
			for (R int t = 0; t < 26; ++ t)
				for (R int v : to[y][t]) 
					if (g[x][v][t] > f[x][y]) {
						g[x][v][t] = f[x][y] + 1;
						pg[x][v][t] = (Link){x, y, 0};
						q2.push((Link){x, v, t}); 
					}
		} else {
			x = q2.front().l, y = q2.front().r, w = q2.front().c;
			q2.pop();
			for (R int u : pre[x][w]) 
				if (f[u][y] > g[x][y][w] + 1) {
					f[u][y] = g[x][y][w] + 1;
					pf[u][y] = (Link){x, y, w};
					q1.push((Link){u, y, 0});
				}
		}
	}
	Q = read() - 1, x = read();
	while (Q --) {
		y = read();
		if (f[x][y] == INF) {
			puts("-1"), x = y;
			continue;
		}
		Output(x, y), x = y;
	}
	return 0;
}