3538: [Usaco2014 Open]Dueling GPS (SPFA)

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三次SPFA，第一次和第二次反向建图，求出任意点到终点最短路，第三次以报警次数为关键字进行SPFA。
#include<algorithm>  #include<iostream>  #include<cstring>  #include<cstdio>  #define inf 0x7fffffff  #define MAXN 100001using namespace std;inline int read() {    int x = 0, f = 1;    char ch = getchar();    while (ch < '0' || ch > '9') {        if (ch == '-')f = -1;        ch = getchar();    }    while (ch >= '0' && ch <= '9') {        x = x * 10 + ch - '0';        ch = getchar();    }    return x*f;}struct edge {    int to, next, v1, v2;} e[MAXN], d[MAXN];int n, m, cnt, ans, u[MAXN], v[MAXN], w1[MAXN], w2[MAXN], d1[10001], d2[10001], dis[10001], head[10001], h[10001];void ins(int u, int v, int w1, int w2) {    e[++cnt] = (edge){v, head[u], w1, w2};    head[u] = cnt;}void spfa1() {    int q[MAXN], t = 0, w = 0;    bool inq[10001];    memset(inq, 0, sizeof (inq));    memset(d1, 127, sizeof (d1));    d1[n] = 0;    q[0] = n;    inq[n] = 1;    while (t <= w) {        int now = q[t++];        for (int i = head[now]; i; i = e[i].next) {            if (d1[now] + e[i].v1 < d1[e[i].to]) {                d1[e[i].to] = d1[now] + e[i].v1;                if (!inq[e[i].to]) {                    q[++w] = e[i].to;                    inq[e[i].to] = 1;                }            }        }        inq[now] = 0;    }}void spfa2() {    int q[MAXN], t = 0, w = 0;    bool inq[10001];    memset(inq, 0, sizeof (inq));    memset(d2, 127, sizeof (d2));    d2[n] = 0;    q[0] = n;    inq[n] = 1;    while (t <= w) {        int now = q[t++];        for (int i = head[now]; i; i = e[i].next) {            if (d2[now] + e[i].v2 < d2[e[i].to]) {                d2[e[i].to] = d2[now] + e[i].v2;                if (!inq[e[i].to]) {                    q[++w] = e[i].to;                    inq[e[i].to] = 1;                }            }        }        inq[now] = 0;    }}void spfa3() {    int q[MAXN], t = 0, w = 0;    bool inq[10001];    memset(inq, 0, sizeof (inq));    memset(dis, 127, sizeof (dis));    dis[1] = 0;    q[0] = 1;    inq[1] = 1;    while (t <= w) {        int now = q[t++];        for (int i = h[now]; i; i = d[i].next) {            if (dis[now] + d[i].v1 < dis[d[i].to]) {                dis[d[i].to] = dis[now] + d[i].v1;                if (!inq[d[i].to]) {                    q[++w] = d[i].to;                    inq[e[i].to] = 1;                }            }        }        inq[now] = 0;    }}int main() {    n = read();    m = read();    for (int i = 1; i <= m; i++) {        u[i] = read();        v[i] = read();        w1[i] = read();        w2[i] = read();        ins(v[i], u[i], w1[i], w2[i]);    }    spfa1();    spfa2();    for (int i = 1; i <= m; i++) {        d[i].to = v[i];        d[i].next = h[u[i]];        h[u[i]] = i;        if (d1[v[i]] + w1[i] > d1[u[i]])d[i].v1++;        if (d2[v[i]] + w2[i] > d2[u[i]])d[i].v1++;    }    spfa3();    printf("%d", dis[n]);    return 0;}
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