0-龙8国际

1因此如果把距离改成可能是0或者1的时候，bfs就可能不会再求出最短距离了，比如当前有一个离当前点距离是1的点待入队列，后续还有一个距离为0的点待入队列，这是完全可能的，但是因为距离是1的会先入队列，距离是0的点会后入队列，从而就破坏了bfs的正确性基于的事实：后入队列的点的离起点的距离一定比先入队列的点离起点的距离远(这里是单调不减)。但是我们可以这样：把队列换成双端队列deque，新的点入队列时，让距离为0的点插入队头，让距离为1的点插入队尾。

龙8唯一官网的版权声明：本文转载「魔术师的徒弟」的原创文章。
原文链接：/cs_opy/article/details/125052319
**例子

**
e - rystal switches
题目：

上代码：
package com.hgs.atcoder.abc.contest277.e;

/**

• youtsuha
• 1.0
• reate by 2022/11/12 19:58
• /

import java.util.;
import java.io.;
public class main {
static fastscanner cin;
static printwriter cout;
static int [][] dp;
private static void init()throws ioexception {
cin = new fastscanner(system.in);
cout = new printwriter(system.out);
}

private static void close(){
    cout.close();
}
static int n, m, k;
static class node{
    int a, b, c;
    //[]
    public node(int a, int b, int c) {
        this.a = a;
        this.b = b;
        this.c = c;
    }
}
static list e[];
static int ans = (int) 1e9;
static int inf = (int) 1e9;
static boolean isswitch[];

// static boolean dfs(int x, int fa, int rot, int dep){
//
// }
private static void sol()throws ioexception {
n = cin.nextint(); m = cin.nextint(); k = cin.nextint();
dp = new int[n][2];
// arrays.fill(dp[0],inf);
// arrays.fill(dp[1],inf);
for(int j = 0; j < 2; j ) {
for(int i = 0; i < n; i ){
//cout.print(dp[i][j] " ");
dp[i][j] = inf;
}
// cout.println("");
}
e = new arraylist[n];
isswitch = new boolean[n];
for(int i = 0; i < n; i ) {
e[i] = new arraylist<>();
}
for(int i = 0; i < m; i ) {
int a = cin.nextint(), b = cin.nextint(), c = cin.nextint();
a--; b--;
e[a].add(new node(b,c,0));
e[b].add(new node(a,c,0));
}
for(int i = 0; i < k; i ) {
int x = cin.nextint(); x--;
isswitch[x] = true;
}
// dfs(0,-1,0, 0);
priorityqueue que = new priorityqueue<>((a,b)->a.c - b.c);
dp[0][0] = 0;
que.add(new node(0,0,0));
while(!que.isempty()){
int x = que.peek().a, d = que.peek().c, rot= que.peek().b;
que.poll();
if(dp[x][rot] > d) {
continue;
}
for(int i = 0; i < e[x].size(); i ) {
int v = e[x].get(i).a, p = e[x].get(i).b;
int nxt = (p rot) % 2;
if(nxt % 2 == 1){
if(dp[v][rot] > d 1){
dp[v][rot] = math.min(dp[v][rot], d 1);
que.add(new node(v,rot,d 1));
}
}else if(isswitch[x]){
nxt = (rot 1) % 2;
if(dp[v][nxt] > d 1){
dp[v][nxt] = math.min(dp[v][nxt], d 1);
que.add(new node(v,nxt, d 1));
}
}
}
}
int ans = inf;
if(dp[n-1][0] != inf) {
ans = math.min(ans, dp[n-1][0]);
}if(dp[n-1][1] != inf) {
ans = math.min(ans, dp[n-1][1]);
}
if(ans == inf) {
cout.println(-1);
}else {
cout.println(ans);
}
}
public static void main(string[] args) throws ioexception {
init();
sol();
close();
}
}
class fastscanner {
bufferedreader br;
stringtokenizer st = new stringtokenizer("");

public fastscanner(inputstream s) {
    br = new bufferedreader(new inputstreamreader(s));
}
public fastscanner(string s) throws filenotfoundexception {
    br = new bufferedreader(new filereader(new file(s)));
}
public string next() throws ioexception {
    while (!st.hasmoretokens()){
        try {
            st = new stringtokenizer(br.readline());
        } catch (ioexception e) { e.printstacktrace(); }
    }
    return st.nexttoken();
}
public int nextint() throws ioexception {
    return integer.parseint(next());
}
public long nextlong() throws ioexception {
    return long.parselong(next());
}
public double nextdouble() throws ioexception {
    return double.parsedouble(next());
}

}

****此代码转载
scau_sleep（今天写bug了吗？的博客