UVA 515 King

差分约束的版。第一次接触这个算法。这里记录一下

理解代码就看这里吧 http://www.cnblogs.com/scau20110726/archive/2012/11/29/2795153.html 感觉写的挺易懂的。跟下面的代码也出入不大

#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <stack>
#include <queue>
#include <cctype>
#include <cstdio>
#include <string>
#include <vector>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
#define LL long long
#define PI 3.1415926535897932626
using namespace std;
int gcd(int a, int b) {return a % b == 0 ? b : gcd(b, a % b);}
#define MAXN 210
int N,M,cnt;
int head[MAXN];
struct node
{
    int v,w;
    int next;
}edge[MAXN * 4];
bool used[MAXN];
int dis[MAXN],num[MAXN];
bool inq[MAXN];
void read()
{
    cnt = 0;
    memset(head,-1,sizeof(head));
    memset(used,false,sizeof(used));
    scanf("%d",&M);
    while (M--)
    {
        char op[10]; int u,v,k;
        scanf("%d%d%s%d",&u,&v,op,&k);
        v += u;
        u --;
        used[u] = used[v] = true;
        if (strcmp(op,"gt") == 0)
        {
            k++;
            edge[cnt].v = u;
            edge[cnt].w = -1 * k;
            edge[cnt].next = head[v];
            head[v] = cnt++;
        }
        else
        {
            k--;
            edge[cnt].v = v;
            edge[cnt].w = k;
            edge[cnt].next = head[u];
            head[u] = cnt++;
        }
    }
    used[N + 1] = true;
    for (int i = 0; i <= N; i++)
    {
        if (!used[i]) continue;
        edge[cnt].v = i;
        edge[cnt].w = 0;
        edge[cnt].next = head[N + 1];
        head[N + 1] = cnt ++;
    }
}
bool SPFA()
{
    memset(dis,0x3f,sizeof(dis));
    memset(inq,false,sizeof(inq));
    memset(num,0,sizeof(num));
    queue<int>q;
    while (!q.empty()) q.pop();
    q.push(N + 1);
    dis[N + 1] = 0;
    num[N + 1] = 1;
    while (!q.empty())
    {
        int u = q.front();q.pop();
        inq[u] = false;
        for (int i = head[u]; i != -1; i = edge[i].next)
        {
            int v = edge[i].v , w = edge[i].w;
            if (dis[v] > dis[u] + w)
            {
                dis[v] = dis[u] + w;
                if (!inq[v])
                {
                    inq[v] = true;
                    q.push(v);
                    num[v] ++;
                    if (num[v] > N + 1) return true;
                }
            }
        }
    }
    return false;
}
int main()
{
    while (scanf("%d",&N) != EOF)
    {
        if (N == 0) break;
        read();
        if (SPFA()) puts("successful conspiracy");
        else puts("lamentable kingdom");
    }
    return 0;
}

另外贴出SPFA的DFS判负环代码记录一下

int spfa_dfs(int u)
{
    vis[u]=1;
    for(int k=first[u]; k!=-1; k=e[k].next)  //遍历顶点u的邻接表
    {
        int v=e[k].v , w=e[k].w;
        if( d[u]+w < d[v])
        {    
            d[v]=d[u]+w;
            if(!vis[v])
            {
                if(spfa_dfs(v))
                    return 1;
            }
            else return 1;
        }
    }
    vis[u]=0;
    return 0;
}