推荐几个比较好的博客：https://blog.csdn.net/whereisherofrom/article/details/78922648 最短路和差分约束
http://www.cnblogs.com/void/archive/2011/08/26/2153928.html 差分约数系统详解
https://blog.csdn.net/xuezhongfenfei/article/details/8685313 差分约束系统
SPFA最短路模板：
1 #include<cstdio> 2 #include<cstring> 3 #include<algorithm> 4 #include<vector> 5 #include<queue> 6 using namespace std; 7 const int maxn=1010; 8 const int inf=1e9; 9 struct edge{ 10 int v,cost; 11 edge(int _v=0,int _cost=0):v(_v),cost(_cost) {} 12 }; 13 vector<edge>E[maxn]; 14 bool vis[maxn]; 15 int cnt[maxn],dist[maxn],s,n; 16 17 void addedge(int u,int v,int w) 18 { 19 E[u].push_back(edge(v,w)); 20 } 21 22 bool SPFA() 23 { 24 memset(vis,false,sizeof(vis)); 25 memset(cnt,0,sizeof(cnt)); 26 for ( int i=1;i<=n;i++ ) dist[i]=inf; 27 vis[s]=true; 28 dist[s]=0; 29 queue<int>que; 30 que.push(s); 31 cnt[s]=1; 32 while ( !que.empty() ) { 33 int u=que.front(); 34 que.pop(); 35 vis[u]=false; 36 for ( int i=0;i<E[u].size();i++ ) { 37 int v=E[u][i].v; 38 int cost=E[u][i].cost; 39 if ( dist[v]>dist[u]+cost ) { 40 dist[v]=dist[u]+cost; 41 if ( !vis[v] ) { 42 vis[v]=true; 43 que.push(v); 44 if ( ++cnt[v]>n ) return false; 45 } 46 } 47 } 48 } 49 return true; 50 }