Poj 1364 King differential constraint finding negative ring

Well, although it's a water question + template question, I still learned a lot and record it.

First, the inequality given in the question is less than, but the difference constraint system can only handle situations where the value is less than or equal to, so it is necessary to convert it into a situation where the value is less than or equal. The integer processing method is very simple =

The next step is to find the negative ring. In fact, you don't need to consider the graph connection. You just need to set the D of all vertices to 0 at the beginning and then push them into the queue.

PS: This method can also be used to deal with the problem of the shortest path of multiple source points.

#include <cstdio>#include <cstring>#include <cmath>#include <algorithm>#include <climits>#include <string>#include <iostream>#include <map>#include <cstdlib>#include <list>#include <set>#include <queue>#include <stack>using namespace std;typedef long long LL;const int maxn = 105;const int maxm = 5005;int first[maxn],nxt[maxm],v[maxm],w[maxm];int d[maxn],n,m,ecnt,cnt[maxn];bool inq[maxn];void adde(int _u,int _v,int _w) {    v[ecnt] = _v; w[ecnt] = _w;    nxt[ecnt] = first[_u];    first[_u] = ecnt;    ecnt++;}void solve() {    bool bad = false;    queue<int> q;    for(int i = 0;i <= n;i++) {        d[i] = 0;        cnt[i] = 1;        inq[i] = true;        q.push(i);    }    while(!q.empty() && !bad) {        int x = q.front(); q.pop();        inq[x] = false;        for(int i = first[x];i != -1;i = nxt[i]) {            if(d[v[i]] > d[x] + w[i]) {                if(!inq[v[i]]) {                    inq[v[i]] = true;                    cnt[v[i]]++;                    q.push(v[i]);                    if(cnt[v[i]] > n + 2) {                        bad = true;                        break;                    }                }                d[v[i]] = d[x] + w[i];            }        }    }    if(bad) puts("successful conspiracy");    else puts("lamentable kingdom");}int main() {    while(scanf("%d",&n),n) {        ecnt = 0;        char sig[16];        scanf("%d",&m);        memset(first,-1,sizeof(first));        memset(nxt,-1,sizeof(nxt));        for(int i = 0;i < m;i++) {            int a,b,c;            scanf("%d %d %s %d",&a,&b,sig,&c);            if(sig[0] == ‘g‘) adde(b + a,a - 1,-c - 1);            else adde(a - 1,b + a,c - 1);        }        /*        for(int i = 1;i <= n;i++) {            adde(i,i - 1,0);        }        */        solve();    }    return 0;}