HDU 3592 World Exhibition (differential constraint)

The question ：n Individuals in order 1-n line up , Can be arranged side by side , give x To the relationship , The distance between two is no more than D; give y To the relationship , The distance between two is not less than D, seek 1 To n The longest distance of .

Answer key ： Difference constraint
Seek the farthest , run spfa shortest path .

The difference constraint equation can be established according to the meaning of the question .
Because of side by side , So the distance limit between two adjacent people is ≤0.

Be careful inf Output -2.

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
#include<algorithm>
#include<queue>
#include<stack>
#include<cmath>
#include<vector>
#include<fstream>
#include<set>
#include<map>
#include<sstream>
#include<iomanip>
#define ll long long
#define pii pair<int, int>
using namespace std;
const int maxn = 1e3 + 5;
const int maxm = 3e4 + 5;
int t, n, x, y, a, b, D;
struct node {
    
    int v, nxt, w;
}edge[maxm];
int vis[maxn], d[maxn], head[maxn], mark[maxn], k, s;
void add(int u, int v, int w) {
    
    edge[++k].nxt = head[u];
    edge[k].v = v;
    edge[k].w = w;
    head[u] = k;
}
bool spfa() {
    
    for (int i = 1; i <= n; i++) {
    
        vis[i] = mark[i] = 0;
        d[i] = 0x3f3f3f3f;
    }
    queue<int>q;
    q.push(s);
    mark[s] = vis[s] = 1;
    d[s] = 0;
    while (!q.empty()) {
    
        int u = q.front(); q.pop();
        vis[u] = 0;
        for (int i = head[u]; i; i = edge[i].nxt) {
    
            int v = edge[i].v, w = edge[i].w;
            if (d[v] > d[u] + w) {
    
                d[v] = d[u] + w;
                if (vis[v]) continue;
                vis[v] = 1;
                if(++mark[v] > n) return false;  // Negative loop  n+1 Only above can there be a negative ring 
                q.push(v);
            }
        }
    }
    return true;
}
int main() {
    
	scanf("%d", &t);
	while (t--) {
    
        k = 0;
        memset(head, 0, sizeof(head));
		scanf("%d%d%d", &n, &x, &y);
        for (int i = 2; i <= n; i++) add(i, i - 1, 0);
		for (int i = 1; i <= x; i++) {
    
			scanf("%d%d%d", &a, &b, &D);
            add(a, b, D);
		}
        for (int i = 1; i <= y; i++) {
    
            scanf("%d%d%d", &a, &b, &D);
            add(b, a, -D);
        }
        s = 1;
        if (spfa()) {
    
            printf("%d\n", d[n] == 0x3f3f3f3f ? -2 : d[n]);
        }
        else puts("-1");
	}
	return 0;
}