POJ - 3259 - Wormholes = SPFA

http://poj.org/problem?id=3259

看见500的数据量莽了一发Floyd，还T了。讲道理应该不至于的，换个快读试试。

#include<algorithm>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<map>
#include<set>
#include<stack>
#include<string>
#include<queue>
#include<vector>
using namespace std;
typedef long long ll;

const int MAXN = 500;
int dis[MAXN + 5][MAXN + 5];

int main() {
#ifdef Yinku
    freopen("Yinku.in", "r", stdin);
#endif // Yinku
    int t;
    scanf("%d", &t);
    while(t--) {
        memset(dis, 0x3f, sizeof(dis));
        int n, m, l;
        scanf("%d%d%d", &n, &m, &l);
        for(int i = 1; i <= n; ++i) {
            dis[i][i] = 0;
        }
        for(int i = 1; i <= m; ++i) {
            int u, v, w;
            scanf("%d%d%d", &u, &v, &w);
            dis[u][v] = min(dis[u][v], w);
            dis[v][u] = min(dis[v][u], w);
        }
        for(int i = 1; i <= l; ++i) {
            int u, v, w;
            scanf("%d%d%d", &u, &v, &w);
            dis[u][v] = min(dis[u][v], -w);
        }
        bool suc = 0;
        for(int k = 1; k <= n; ++k) {
            for(int i = 1; i <= n; ++i) {
                for(int j = 1; j <= n; ++j) {
                    dis[i][j] = min(dis[i][j], dis[i][k] + dis[k][j]);
                }
                if(dis[i][i] < 0) {
                    suc = 1;
                    break;
                }
            }
            if(suc)
                break;
        }
        puts(suc ? "YES" : "NO");
    }
}

但是假如图本身连通的话，写SPFA就可以了。

#include<algorithm>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<map>
#include<set>
#include<stack>
#include<string>
#include<queue>
#include<vector>
using namespace std;
typedef long long ll;

const int MAXN = 505;
const int MAXM = 10005;

int top;
int head[MAXN];
struct Edge {
    int v, nxt;
    int w;
} edge[MAXM];

void init() {
    top = 0;
    memset(head, -1, sizeof(head));
}

void add_edge(int u, int v, int w) {
    ++top;
    edge[top].v = v;
    edge[top].w = w;
    edge[top].nxt = head[u];
    head[u] = top;
}

bool vis[MAXN];
int cnt[MAXN];
int dis[MAXN];

queue<int>q;
bool spfa(int s, int n) {
    memset(vis, 0, sizeof(vis));
    memset(cnt, 0, sizeof(cnt));
    for(int i = 0; i < MAXN; ++i)
        dis[i] = 0x3f3f3f3f;

    while(!q.empty())
        q.pop();
    q.push(s);
    vis[s] = 1;
    cnt[s] = 1;
    dis[s] = 0;

    while(!q.empty()) {
        int u = q.front();
        q.pop();
        vis[u] = 0;
        for(int i = head[u]; i != -1; i = edge[i].nxt) {
            int v = edge[i].v;
            if(dis[v] > dis[u] + edge[i].w) {
                dis[v] = dis[u] + edge[i].w;
                if(!vis[v]) {
                    vis[v] = 1;
                    q.push(v);
                    if(++cnt[v] > n)
                        return 0;
                }
            }
        }
    }
    return 1;
}

int main() {
#ifdef Yinku
    freopen("Yinku.in", "r", stdin);
#endif // Yinku
    int t;
    scanf("%d", &t);
    while(t--) {
        int n, m, l;
        scanf("%d%d%d", &n, &m, &l);
        init();
        for(int i = 1; i <= m; ++i) {
            int u, v, w;
            scanf("%d%d%d", &u, &v, &w);
            add_edge(u, v, w);
            add_edge(v, u, w);
        }
        for(int i = 1; i <= l; ++i) {
            int u, v, w;
            scanf("%d%d%d", &u, &v, &w);
            add_edge(u, v, -w);
        }
        bool suc = !spfa(1, n);
        puts(suc ? "YES" : "NO");
    }
}

速度172ms，可能可以试试优化。

带SLF优化的SPFA，47ms，这么快是因为POJ抖了吗？

#include<algorithm>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<map>
#include<set>
#include<stack>
#include<string>
#include<queue>
#include<vector>
using namespace std;
typedef long long ll;

const int MAXN = 505;
const int MAXM = 10005;

int top;
int head[MAXN];
struct Edge {
    int v, nxt;
    int w;
} edge[MAXM];

void init() {
    top = 0;
    memset(head, -1, sizeof(head));
}

void add_edge(int u, int v, int w) {
    ++top;
    edge[top].v = v;
    edge[top].w = w;
    edge[top].nxt = head[u];
    head[u] = top;
}

bool vis[MAXN];
int cnt[MAXN];
int dis[MAXN];

deque<int>q;
bool spfa(int s, int n) {
    memset(vis, 0, sizeof(vis));
    memset(cnt, 0, sizeof(cnt));
    for(int i = 0; i < MAXN; ++i)
        dis[i] = 0x3f3f3f3f;

    q.clear();
    q.push_back(s);
    vis[s] = 1;
    cnt[s] = 1;
    dis[s] = 0;

    while(!q.empty()) {
        int u = q.front();
        q.pop_front();
        vis[u] = 0;
        for(int i = head[u]; i != -1; i = edge[i].nxt) {
            int v = edge[i].v;
            if(dis[v] > dis[u] + edge[i].w) {
                dis[v] = dis[u] + edge[i].w;
                if(!vis[v]) {
                    vis[v] = 1;
                    //SLF优化 据说15%~20%
                    if(!q.empty() && dis[v] >= dis[q.front()])
                        q.push_back(v);
                    else
                        q.push_front(v);
                    if(++cnt[v] > n)
                        return 0;
                }
            }
        }
    }
    return 1;
}

int main() {
#ifdef Yinku
    freopen("Yinku.in", "r", stdin);
#endif // Yinku
    int t;
    scanf("%d", &t);
    while(t--) {
        int n, m, l;
        scanf("%d%d%d", &n, &m, &l);
        init();
        for(int i = 1; i <= m; ++i) {
            int u, v, w;
            scanf("%d%d%d", &u, &v, &w);
            add_edge(u, v, w);
            add_edge(v, u, w);
        }
        for(int i = 1; i <= l; ++i) {
            int u, v, w;
            scanf("%d%d%d", &u, &v, &w);
            add_edge(u, v, -w);
        }
        bool suc = !spfa(1, n);
        puts(suc ? "YES" : "NO");
    }
}