POJ 3114 Countries in War

 

 

水。。。

CODE：

 

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <queue>
using namespace std;

const int MAXN = 510;
const int MAXM = 510*510;
const int INF = 0x3f3f3f3f;

struct Edge
{
    int v, w;
    int next;
}edge[MAXM], edge2[MAXM];

int n, m;
int cnt, cnt2;
int scnt, top, tot;

int first[MAXN], low[MAXN], dfn[MAXN], stack[MAXN], ins[MAXN];
int d[MAXN];
int first2[MAXN];
int belong[MAXM];

char str[51] = "Nao e possivel entregar a carta";

void init()
{
    cnt = cnt2 = 0;
    scnt = top = tot = 0;
    memset(first, -1, sizeof(first));
    memset(first2, -1, sizeof(first2));
    memset(dfn, 0, sizeof(dfn));
    memset(ins, 0, sizeof(ins));
}

void read_graph(int u, int v, int w)
{
    edge[cnt].v = v, edge[cnt].w = w;
    edge[cnt].next = first[u], first[u] = cnt++;
}

void read_graph2(int u, int v, int w)
{
    edge2[cnt2].v = v, edge2[cnt2].w = w;
    edge2[cnt2].next = first2[u], first2[u] = cnt2++;
}

void dfs(int u)
{
    int v;
    dfn[u] = low[u] = ++tot;
    stack[top++] = u;
    ins[u] = 1;
    for(int e = first[u]; e != -1; e = edge[e].next)
    {
        v = edge[e].v;
        if(!dfn[v])
        {
            dfs(v);
            low[u] = min(low[u], low[v]);
        }
        else if(ins[v])
        {
            low[u] = min(low[u], dfn[v]);
        }
    }
    if(dfn[u] == low[u])
    {
        scnt++;
        do
        {
            v = stack[--top];
            belong[v] = scnt;
            ins[v] = 0;
        }while(u != v);
    }
}

void Tarjan()
{
    for(int v = 1; v <= n; v++) if(!dfn[v])
        dfs(v);
}

void spfa(int src)
{
    queue<int> q;
    bool inq[MAXN] = {0};
    for(int i = 1; i <= n; i++) d[i] = (i == src) ? 0:INF;
    q.push(src);
    while(!q.empty())
    {
        int x = q.front(); q.pop();
        inq[x] = 0;
        for(int e = first2[x]; e != -1; e = edge2[e].next)
        {
            int v = edge2[e].v , w = edge2[e].w;
            if(d[v] > d[x] + w)
            {
                d[v] = d[x] + w;
                if(!inq[v])
                {
                    inq[v] = 1;
                    q.push(v);
                }
            }
        }
    }
}

int read_case()
{
    init();
    scanf("%d", &n);
    if(!n) return 0;
    scanf("%d", &m);
    while(m--)
    {
        int u, v, w;
        scanf("%d%d%d", &u, &v, &w);
        read_graph(u, v, w);
    }
    return 1;
}

void build()
{
    Tarjan();
    for(int u = 1; u <= n; u++)
    {
        for(int e = first[u]; e != -1; e = edge[e].next)
        {
            int v = edge[e].v, w = edge[e].w;
            if(belong[u] != belong[v])
            {
                read_graph2(u, v, w);
            }
            else read_graph2(u, v, 0);
        }
    }
}

void solve()
{
    int q;
    build();
    scanf("%d", &q);
    while(q--)
    {
        int s, e;
        scanf("%d%d", &s, &e);
        spfa(s);
        if(d[e] != INF) printf("%d\n", d[e]);
        else printf("%s\n", str);
    }
    printf("\n");
}

int main()
{
    while(read_case())
    {
        solve();
    }
    return 0;
}