记录一个洛谷评测机上的问题

下面这个代码是给普通spfa，我本想用它来测试spfa面对高压数据下的表现，但是让人困惑的是洛谷的评测机给出了WA的评分，这让我以为是算法哪里除了问题，检查半天没检查出来，发到群里，有人指出这是手写队列导致溢出，这一点我一开始是想到了的，我没想到溢出导致了WA，这里记录一下，以后记得溢出也会WA

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
using namespace std;
#define Max 500000
#define Inf (0x7fffffff/2)
int first0[Max + 1], next0[Max + 1];
int v[Max + 1], w[Max + 1];
int dist[Max + 1], book[Max + 1];
int queue[Max + 1],head=0,tail=0;
int read() {
	int x = 0, f = 1; char c = getchar();
	while (c < '0' || c > '9') { if (c == '-')f = -1; c = getchar(); }
	while (c >= '0' && c <= '9') { x = x * 10 + c - '0'; c = getchar(); }
	return x * f;
}
int main()
{
	int N, M, S; cin >> N >> M >> S;
	//初始化邻接表
	for (int i = 1; i <= M; i++){
		first0[i] = next0[i] = -1;
	}
	//初始化dist
	for (int i = 1; i <= N; i++){
		dist[i] = Inf;
	}
	//读入边
	/*
		5 5 1
2 3 2 1 2 -3 1 5 5 4 5 2 3 4 3
	*/
	register int u;
	for (int i = 1; i <= M; i++){
		u = read(), v[i] = read(), w[i] = read();
		next0[i] = first0[u];
		first0[u] = i;
	}
	//spfa
	dist[S] = 0;
	book[S] = 1;
	queue[tail++] = S;
	while (head != tail) {
		int k = queue[head++];
		for (int e = first0[k]; e!=-1; e=next0[e]){
			if (dist[k] + w[e] < dist[v[e]]) {
				dist[v[e]] = dist[k] + w[e];
				if (!book[v[e]]) {
					//if (head != tail && v[k] < queue[head] && head>=1) {
					//	queue[--head] = v[k];
					//}
					queue[tail++] = v[e];
					book[v[e]] = 1;
				}
			}
		}
		book[k] = 0;
	}
	//output
	for (int i = 1; i <= N; i++){
		if(dist[i]!=Inf)
			printf("%d ", dist[i]);
		else printf("%d ",0x7fffffff);
	}
    return 0;
}