Poj 3169 layout difference Constraint

After doing this question, I feel that my understanding of the difference constraint has deepened.

For the question of whether the value required by the difference constraint is the maximum value or the minimum value, when the minimum value is obtained, you can reverse edge creation to find the shortest path, you can also convert it to the-B> = x constraint and then find the longest path. When the maximum value is obtained, you can directly find the shortest path. If the target distance is INF, it indicates any length.

#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 = 10000 + 5;const int maxm = 500000 + 5;const int INF = INT_MAX / 4;int first[maxn],nxt[maxm],d[maxn],v[maxm],w[maxm];int N,ML,MD,qcnt[maxn],ecnt;bool inq[maxn];void adde(int _u,int _v,int _w) {    //printf("adde %d %d %d\n",_u,_v,_w);    v[ecnt] = _v;   w[ecnt] = _w;    nxt[ecnt] = first[_u];    first[_u] = ecnt;    ecnt++;}void solve() {    bool bad = false;    for(int i = 0;i <= N;i++) {        d[i] = INF;        inq[i] = false;        qcnt[i] = 0;    }    d[1] = 0;    inq[1] = true;    queue<int> q;    q.push(1);    qcnt[1] = 1;    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]) {                d[v[i]] = d[x] + w[i];                if(!inq[v[i]]) {                    q.push(v[i]);                    inq[v[i]] = true;                    qcnt[v[i]]++;                    if(qcnt[v[i]] > N + 1) {                        bad = true; break;                    }                }            }        }    }    //for(int i = 0;i <= N;i++) printf("%d ",d[i]); putchar(‘\n‘);    //for(int i = 0;i <= N;i++) printf("%d ",qcnt[i]); putchar(‘\n‘);    if(bad == true) puts("-1");    else if(d[N] >= INF) puts("-2");    else printf("%d\n",d[N]);}int main() {    while(~scanf("%d%d%d",&N,&ML,&MD)) {        ecnt = 0;        memset(first,-1,sizeof(first));        memset(nxt,-1,sizeof(nxt));        for(int i = 1;i <= ML;i++) {            int a,b,c; scanf("%d%d%d",&a,&b,&c);            adde(a,b,c);        }        for(int i = 1;i <= MD;i++) {            int a,b,c; scanf("%d%d%d",&a,&b,&c);            adde(b,a,-c);        }        for(int i = 1;i <= N;i++) {            adde(i,i - 1,0);        }        solve();    }    return 0;}