【题目链接】
【算法】
差分约束系统，SPFA判负环
【代码】
#include <algorithm> #include <bitset> #include <cctype> #include <cerrno> #include <clocale> #include <cmath> #include <complex> #include <cstdio> #include <cstdlib> #include <cstring> #include <ctime> #include <deque> #include <exception> #include <fstream> #include <functional> #include <limits> #include <list> #include <map> #include <iomanip> #include <ios> #include <iosfwd> #include <iostream> #include <istream> #include <ostream> #include <queue> #include <set> #include <sstream> #include <stdexcept> #include <streambuf> #include <string> #include <utility> #include <vector> #include <cwchar> #include <cwctype> #include <stack> #include <limits.h> using namespace std; #define MAXN 1010 #define MAXM 200010 struct Edge { int to,w,nxt; } e[MAXM]; int i,n,m,a,b,c,tot; int dis[MAXN],head[MAXN]; char opt[5]; inline void add(int u,int v,int w) { tot++; e[tot] = (Edge){v,w,head[u]}; head[u] = tot; } inline bool spfa() { int i,cur,v,w; queue<int> q; static bool inq[MAXN]; static int cnt[MAXN]; for (i = 1; i <= n; i++) { dis[i] = 0; q.push(i); inq[i] = true; cnt[i] = 1; } while (!q.empty()) { cur = q.front(); q.pop(); inq[cur] = false; for (i = head[cur]; i; i = e[i].nxt) { v = e[i].to; w = e[i].w; if (dis[cur] + w > dis[v]) { dis[v] = dis[cur] + w; if (!inq[v]) { inq[v] = true; cnt[v]++; if (cnt[v] > n) return false; q.push(v); } } } } return true; } int main() { while (scanf("%d",&n) != EOF && n) { tot = 0; for (i = 1; i <= n; i++) head[i] = 0; scanf("%d",&m); while (m--) { scanf("%s",&opt); if (strcmp(opt,"P") == 0) { scanf("%d%d%d",&a,&b,&c); add(b,a,c); add(a,b,-c); } else { scanf("%d%d",&a,&b); add(b,a,1); } } if (spfa()) printf("Reliable "); else printf("Unreliable "); } return 0; }